SC_B Study guide

Genetics Study Guide: 

Genetics Study Guide

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In humans, brown eye color is dominant, blue is recessive. A heterozygous brown-eyed man marries a blue-eyed woman. What are the possible genotypes and phenotypes of their offspring? Normal pigmentation is dominant and albino is recessive. If a normal man marries an albino woman and they have a normal boy and an albino girl, what are the genotypes of the parents? B= brown bb= blue B b b b Bb Bb bb bb Genotypes: Bb or bb Phenotypes: brown or blue P= normal pigment pp= albino P p p p Pp Pp pp pp Mom: pp Dad: Pp (carrier)

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3. Cystic fibrosis is an autosomal recessive disorder. If two phenotypically normal parents have a child with cystic fibrosis, what are the genotypes of the two parents, and the child? 4. What is the probability that their next child will also have the disease? C= NORMAL cc= cystic fibrosis C c C c CC Cc Cc cc Mom & Dad: Cc (carriers) Child: cc (have cystic fibrosis) 25 % chance that the child will have cystic fibrosis

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5. Due to incomplete dominance, snapdragons are often blended to make interesting colors. If you crossed a red snapdragon with a white snapdragon, what would be the possible genotypic and phenotypic ratios of the offspring? RR= red RW= pink R R W W RW RW RW RW Genotypes: 100% RW Phenotypes: all pink WW= white

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6. Co-dominance occurs when both alleles in a heterozygote are expressed. Roan is the term for the condition where white hair is mixed in with a base hair color. This is common in horses. If two grey roan horses were crossed, what would be the genotypic and phenotypic ratios of their offspring? RR= red RR’= roan R R ’ R R’ RR RR’ RR’ R’R’ Genotypes: 1:2:1 RR:RR’:R’R’ Phenotypes: 1:2:1 red:roan:white R’R’= white

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7.Red-green color blindness in humans is a sex-linked recessive trait on the X-chromosome. If a color-blind male marries a female with normal vision (that is not a carrier), what percent of their male children will likely be colorblind? XX= normal XX c = Carrier X X X c Y XX c XY XX c XY 0% of children will be colorblind X c X c = colorblind female X c Y = colorblind male

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8. A female who is heterozygous for type A blood marries a man that is type O. What are the possible genotypes and phenotypes of their children? I A I O =mom I O I O = dad I A I O I O I O I A I O I A I O I O I O I O I O Genotypes: 2:2 or 1:1 I A I O :I O I O Phenotypes 1 I A I O : 1I O I O 1 type A 1 type O

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T y t y BS Bs bS bS bS bS BS Bs bS bS BbSS BbSs bbSS bbSS Black/Short Black/Short White/Short White/long

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11.Two heterozygous black short-haired cats mate. What is the probable phenotypic ratio of their offspring? (use data table above for information) 12. If a human baby boy inherits a recessive allele from his mother, in which circumstance would he most likely show the trait coded for by the recessive allele? A. The baby inherits the dominant allele from his father B. The allele is on an autosomal chromosome and the baby is a twin. C. The allele is on the X chromosome. D. The allele is on the Y chromosome. BbSs BbSs x 9 black short : 3 black long : 3 white short : 1 white long

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Dominant Gg Gg Gg Gg Gg gg gg gg gg gg gg gg gg gg gg gg

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15. A tall pea plant sprouts up in a garden away from the rest of the pea plants. You want to know if the pea plant is heterozygous (hybrid) or homozygous dominant (purebred). Describe how you could find out. 16. The prevalence of carriers for Tay -Sachs disease among Ashkenazi Jews is 2/5. If two Ashkenazi Jews marry and have a child, what is the chance that this child would have the recessive Tay -Sachs disease? Test cross: Cross the tea plant (unknown) with a homozygous recessive individual T= tall tt =short t t ? ? All tall, Parent= TT 50% tall, 50% short = Tt

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