GENETIC S UNIT TASK CARDS Grades 7-10 ANSWERS 1 Which of Mendels Laws states that the members of each pair of alleles separate when gametes are formed? Tt Mendels Law of Segregation T t

2 Draw a Punnett square depicting the cross of the F1 generation of Mendels pea plant experiments. P P p PP Pp Pp pp p

3 In Rabbits, the allele B for black hair is dominant over the allele b for brown hair. Calculate the probability of homozygous dominant offspring resulting from a cross between two heterozygous parents. B B b BB Bb Bb bb b

The probability of having homozygous dominant offspring is or 25% 4 In horses, the allele C for a chestnut coat is is dominant to the allele c a gray coat. Calculate the probability of heterozygous offspring resulting from a cross between a heterozygous parent and a homozygous recessive parent. The probability of having heterozygous offspring is or 50% C c c

Cc cc Cc cc c 5 In horses, the allele C for a chestnut coat is is dominant to the allele c a gray coat. A heterozygous stallion and a heterozygous mare have produced three chestnut foals. What is the chance that their next foal will also be chestnut? The probability of having another chestnut foal is or 75%.

C C c CC Cc c Cc cc 6 In eggplant, the allele P for purple eggplants are dominant over the

allele p for white eggplants. Calculate the probability of heterozygous offspring resulting from a cross between a homozygous dominant parent and a homozygous P P recessive parent. The probability of having heterozygous offspring is 100% p p Pp Pp Pp

Pp 7 In pea plants, the allele T for tall pea plants is dominant to the allele t for short plants. Calculate the probability of homozygous dominant offspring from a cross between a heterozygous parent and a homozygous recessive parent. T t The probability of having homozyous dominant offspring is 0%. t Tt tt t

Tt tt 8 In dragons, yellow eyes are dominant to green eyes. Two yellow-eyed dragons mate, and produce three eggs. Of the three hatchlings, one has green eyes. What are the genotypes of the parent dragons? The parent dragons must be heterozygous. Y Y y YY

Yy Yy yy y 9 In Hawaiian Happy Face Spiders, the patterned allele is dominant to the plain allele. A plain spider is crossed with a patterned spider. The patterned spider is heterozygous. Which genotypes are produced among the offspring and in what ratio? Which phenotypes are produced and in what

ratio? P p The genotypic ratio of the offspring is 2:2 heterozygous to homozygous recessive; The phenotypic ratio of the offspring is 2:2 patterned to plain or 50/50. p Pp pp Pp pp

p 10 In Hawaiian Happy Face Spiders, the patterned allele is dominant and the plain allele is recessive. Two patterned heterozygous spiders are crossed. 600 offspring are produced. How many of them are plain? 150 of the offspring would be predicted to be plain.

11 If you resemble one parent more than the other, does that mean that you have inherited more of your genes from that parent? Briefly explain your reasoning. No, you inherit half of your genes from each of your parents. If you resemble one parent more than the other, then you probably inherited more of that parents dominant traits. 12 Which Mendels Law states that two or more pairs of alleles segregate independently of one another during gamete formation, creating at least four different outcomes? Aa Mendels Law of Independent

Assortment Bb A A a a B b B b

13 Which of Mendels laws does this illustration represent? Mendels Principle of Dominance 14 Which of Mendels laws does this illustration represent? Mendels Law of Independent Assortment 15 Which parent, mother or father, determines the

gender of the child? Provide evidence using a punnett square. The father determines the gender of the child. Mothers are XX, they can only give X chromosomes to their children. The father is XY. If he gives the child an X, the child is a girl. If he gives the child a Y then the child is a boy. Mother Fa th er

X X X XX XX XY XY Y 16 In Alaskan malamutes, the dwarf allele is recessive (d), while the normal allele is dominant (D). Show

a test cross in which all of the offspring are phenotypically dominant. D d D Dd Dd Dd Dd d 17

How many traits are being examined in this cross? Which type of cross is demonstrated in this Punnett square? Two traits -- A dihybrid cross. 18 Describe the difference in phenotypes between organisms that exhibit incomplete dominance for a trait vs. organisms that exhibit codominance for a trait. In organisms that exhibit incomplete dominance, the traits blend together like mixing paint. In organisms that exhibit codominance, the traits are

both present; neither is masked by the other. 19 Hair texture typically is incompletely dominant, and can be curly (C), straight (S) or wavy (SC). Construct a Punnett square crossing a curly-haired parent with a wavyhaired parent. Determine all phenotypic ratios of the potential offspring. C S C C CC

CC CS CS 50% of the offspring will show the hybrid trait (wavy); 50% of the offspring will have curly hair. 20 The rhododendron pictured here exhibits which of inheritance pattern for the flower petal color?

Codominance. 21 A cross between a black cat and a tan cat produces a tabby pattern (black and tan fur together). List all the possible phenotypes and in what ratios from a cross between a tabby cat and a black cat. 50% of the kittens would have black fur; 50% of the kittens would have the tabby pattern. B

B T BB BT BB BT B 22 Plant 1 Plant 2

Plant 1 is homozygous for the chevron allele. Plant 2 is homozygous for the oval allele. The chevron and oval alleles are codominant. If plant 1 and plant 2 are crossed, the codominance of the alleles will most likely result in which of the following leaf patterns on the offspring plants? A B C D 23 In humans, there are 3 alleles for blood types: A, B and O. A and B are

codominant, resulting in a third blood type, AB. The O blood type is recessive. If a man who is heterozygous for type B blood marries a woman who has type AB blood, which blood type would their child most likely be? The child would most likely be type B (with a 50% chance). IA IB i IB IAIB I BI B

I Ai IBi 24 In pigeons, three alleles of a single gene govern their feather color. BB= blue feathers BA= ash red feathers bb= chocolate feathers (recessive). Which complex pattern of heredity is this an Multiple alleles. example of? 25 In pigeons, three alleles of a single

gene govern their feather color. BB= blue feathers (dominant) BA= ash red feathers b= chocolate feathers (recessive) Construct a Punnett square crossing a pure ash-red pigeon to a blue pigeon who also carries the recessive allele. Which percentage of the offspring could be expected to be ash-red? 50% of the offspring could be expected to be ash-red. BA BB b

BA BBBA BBBA BAb BAb 26 Which pattern of inheritance does the diagram illustrate? X linked inheritance.

27 A woman who is heterozygous for hemophilia marries a healthy man (does not have hemophilia.) What are the chances that they will have a child with hemophilia? Provide evidence using a punnet square. 28 Hemophilia is an sex linked disorder in which blood clotting proteins are severely reduced; causing excessive bleeding from minor injuries. Given that it the allele for hemophilia is present on the X chromosome, explain how you know the genotype of the father of a hemophiliac woman. Since women inherit the X chromosome from their father (as opposed to the Y), and men only have one X chromosome. Therefore,

if the woman is hemophilic her father must also be hemophilic given that it is a recessive disorder. 29 In cats, the genotype XB is black, XBXO is calico, and XO is orange. The gene codominant and is located on the X chromosome, making it a sex-linked trait. If a calico female mates with a black male, what offspring would be expected? XB XB Y Xb XBXB XBXb

XBY X bY The offspring that would be expected are black and calico females, and black and orange males. 30 In cats, the genotype XB is black, XBXO is calico, and XO is orange. The gene codominant and is located on the X chromosome, making it a sex-linked trait. Refer to card #32. Explain why there could never be any male calico cats. There can never be a calico

male cat because two alleles are required. Since the alleles are X-linked, two X chromosomes are needed. 31 I. I!. I!I. IV. Is this likely a pedigree for a dominant or recessive trait/disorder? Explain how you know using examples from the pedigree.

The disorder is recessive. I-1 has the disorder, and I-2 does not; all of their children are carriers/heterozygous, but they do not have the disorder/trait. 32 I. I!. I!I. IV. Is this likely a pedigree for a dominant or recessive trait/disorder? Explain how you know

using examples from the pedigree. The disorder is dominant. One possible explanation is persons II-4 and II-5. The both have the trait but their son (person III-5) does not. If this were a recessive trait, all their children would have it. 33 In certain portions of the population, there is a lethal genetic disease called Tay Sachs disease. Tay Sachs results in destruction of the nervous system. This disease is caused by a recessive allele of a single gene. Why does this disease persist, even though it is fatal long before the afflicted individual reaches reproductive age? (in other words, why doesnt the allele for Tay Sachs disease simply disappear?)

This disorder doesnt disappear from the population because someone who is a carrier (heterozygous) does not have the disease but can pass it to their children. If two parents, who are heterozygous for Tay Sachs, have children, then each of their children have a 25% chance of inheriting two copies of the Tay Sachs gene and thereby having the disease. 34 The diagram shows the positions of the genes for flower color and stem length in a pea plant. The chromosomes represented below will replicate before meiosis. For these two genes, what is the maximum number of different allele combinations that can be formed normally in gametes produced from this

cell? Answer: four Pt, PT, pt, pT 35 In guinea pigs, the allele S for short hair is dominant over the allele s for long hair. Also, the allele B for black hair is dominant over the allele b for brown hair. Which ratio of offspring are expected to be short haired and brown from a cross of two guinea pigs that are both heterozygous for each trait? 3/16 of the offspring. *You may require a dihybrid Punnett square but students should be familiar with the 9:3:3:1 ratio for heterozygous crosses. 36

Explain the difference between polygenic traits and multiple alleles. Provide an example of each. Polygenic Traits: multiple genes control a single trait. This will produce a wide range or gradient of phenotypes. Examples include height & skin color. Multiple Alleles: There are multiple variations of a trait within a population. Examples include human blood types, and rabbit fur color. There are three alleles for blood type in the human population (IA, IB and i) 37 What type of genetic disease is shown below? Translocation 38 What type of genetic disease is shown below?

Nondisjunction 39 Explain how to parents with achondroplasia can have a regular height child. Because achondroplasia is a dominant single gene mutation, parents must only carry 1 allele coding for the condition (be heterozygous). As such, if both parents are heterozygous, there is a 1:4 chance (25%) that their child will be born without the condition. 40 Challenge: Do you really understand independent assortment? Try a Trihybrid! Dominant

Recessive Plant Height Tall (T) Short (t) Pea Texture Round (R) Wrinkled (r) Pea Color Green (G) Yellow (g)

A pea plant with the genotype TtrrGg is crossed with a pea plant with genotype ttRRGg. What percentage of offspring will be tall with green round peas? Show your work on a separate piece of paper. Answer on the next slide 41 Parent 1: TtrrGg TrG, Trg, trG, trg Parent 2: ttRRGg tRG, tRg TrG Trg trG trg tRG

TtRrGG TtRrGg ttRrGG ttRrGg tRg TtRrGg TtRrgg ttRrGg ttRrgg

1/8 TtRrGG 2/8 TtRrGg 1/8 TtRrgg 1/8 ttRrGG 2/8 ttRrGg 1/8 ttRrgg 3/8 Tall with Green, Round Peas

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