Beyond Dominant and Recessive Alleles AND Human Heredity

Beyond Dominant and Recessive Alleles AND Human Heredity Chapter 11-3 Exploring Medelian Genetics AND Chapter 14-1 and 14-2

Incomplete Dominance, Codominance, Multiple Alleles and Polygenic Traits and Human Heredity • Not all genes show simple patterns of dominant and recessive alleles. • In most organism, genetics is more complicated, because the majority of genes have more than two alleles. • Also, many important traits are controlled by more than one gene.

Incomplete Dominance • Neither allele is dominant over another so the heterozygous individual is somewhere in between (blend). • A cross between a red and white Mirabilis plants (called four o'clocks) have pink flowers.

In four o’clock plants, cross a red flower and a white flower. Show the genotype and phenotype for F1. Key: RR=red flowers RW=pink flowers WW=white flowers RR x WWp R R W W Genotype F1 W W =RW 4 Phenotype F1 R RW RW 4 =pink R RW RW F1

In four o’clock plants, cross a pink flower and a pink flower. Show the genotype and phenotype for F1. Key: RR=red flowers RW=pink flowers WW=white flowers RW x RWp R W R W Genotype F1 R W =RR 1 2 =RW 1 =WW R RR RW Phenotype F1 =red 1 W RW WW 2 =pink 1 =white F1

roan hamster Codominance • Both alleles are equally contributing or dominant so each trait is shown. • A cross between a white and black hamster can have a grey appearance due to having BOTH white and black hairs (mix). • These are worked the same as incomplete dominance problems.

Cross a white fur hamster and roan fur hamster. Show the genotype and phenotype for F1. Key: WW = white fur WB = roan fur BB = black fur WW x WBp W W W B What percentage of hamsters are white? Black? Roan? Genotype F1 2 W B =WW 2 =WB W WW WB Phenotype F1 2 =white fur W WW WB 2 =roan fur F1

Test Cross • Test crosses are used to find the genotype of parents. You need to look at the offspring in order to discover the genotype of a parent. • ALWAYS cross the unknown with the known…. (the known is homozygous recessive) • Cross homozygous dominant with homozygous recessive then heterozygous with homozygous recessive

Key: T = Tall pea plant t = short pea plant A tall pea plant was crossed with a short pea plant. All of the offspring were tall….none were short! What is the genotype of the tall pea plant? TT x tt Tt x tt t t t t Tt Tt T Tt Tt T Tt Tt t tt tt T Genotype Phenotype Genotype Phenotype 4 Tt 4 tall 2 Tt 2 tt 2 tall 2 short

Multiple Alleles • Many genes have more than two alleles and are therefore said to have multiple alleles. • This does NOT meant that an individual can have more than two alleles! • It means that more than two possible alleles exist in a population.

Genotype and Phenotype of blood: • AA and AO = type A blood • BB and BO = type B blood • AB = type AB blood • OO = type O blood

If a heterozygous type A person is crossed with a heterozygous type B, show the genotype and and phenotype of the F1 offspring. • Key: • AA and AO = type A blood • BB and BO = type B blood • AB = type AB blood • OO = Type O blood AO x BOp Genotype F1 1 =AB A O B O 1 =AO B O 1 =BO 1 =OO A AB AO Phenotype F1 1 =type AB 1 =type A O BO OO 1 =type B 1 =type O F1

Polygenic Traits • Many traits are produced by the interaction of several genes(example is eye color, skin color, height, facial features) • Traits controlled by two or more genes are said to be polygenic traits, which means “having many genes.” • For example, the wide range of skin color in humans comes about partly because more than four different genes probably control this trait http://www.athro.com/evo/inherit.html

Determination of Gender • What are the chances of a couple having a boy? Girl? Show your work! • Hint: females are xx and males are xy xxxxy % chance of girl? x y 50% x xx xy % chance of boy? x xx xy 50%

Sex Linked Genes • Genes that are carried on the X chromosome are expressed in the male (since his other chromosome is Y) • Example: Red-green colorblindness – recessive trait • Example: Hemophilia – recessive trait

Are you color blind? Let’s take the Ishihara Test for Color Blindness

What numbers do you see? Normal vision = 25 Red-Green Color blind = 25 Normal vision = 29 Red-Green Color blind = spots Normal vision = 45 Red-Green Color blind = spots Normal vision = 56 Red-Green Color blind = 56 Normal vision = 6 Red-Green Color blind = spots Normal vision = 8 Red-Green Color blind = spots

The test below is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

How the world looks to a person with a red/green color deficit (deuteranopia). How the world looks to a person with a blue/yellow color deficit (tritanopia). The world.

As seen by a person with protanopia, another form of red/green deficit. As seen by a person with deuteranopia. Some colorful hats.

Let’s work a problem for sex linked genes showing a cross between a colorblind male and a female carrier (heterozygous).Hint: color blindness is recessive so it will be lower case where normal is capital. Key: XBY = male, normal XbY = male, colorblind XB XB = female, normal XB Xb = female, normal (carrier) Xb Xb = female, colorblind

Key: XBY = male, normal XbY = male, colorblind XB XB = female, normal XB Xb = female, normal (carrier) Xb Xb = female, colorblind colorblind male and a female carrier (heterozygous) XbY x XBXb Genotype: 1 = XBXb 1 = XbXb XB Xb 1 = XBY 1 = XbY Xb XBXb XbXb Phenotype: 1 = female, normal (carrier) 1 = female, colorblind Y XBY XbY 1 = male, normal 1 = male, colorblind

Sex limited traits • Appear only in certain gender • Example: Heavy beard is only in males

Sex influenced traits • Traits that are dominant in one gender and recessive in another • Example: baldness (a woman must have two dominant alleles to be bald and a man only needs one dominant allele

Chromosomal mutations • An organism is missing a chromosome or has an extra chromosome

Nondisjunction during meiosis • If the homologous chromosome do not separate, one cell ends up with an extra chromosome and the other cell is lacking a chromosome. • In somatic (body) cells, its offspring is not affected. • In gametes, the mutation is passed to the offspring.

Nondisjunction during meiosis • Down’s Syndrome = has extra 21st chromosome

Karyotype (picture of chromosomes) • Down’s Syndrome = has extra 21st chromosome

Polyploidy • The nucleus does not divide after it duplicates its DNA. • If it is fertilized, it ends up with an extra set of chromosomes (3n) • In animals it is LETHAL (die) • In plants it makes them grow larger and healthier

Gene Mutations • Will be discussed after we learn about DNA

Homework Problems Set #3 • Rabbit spotted coat (R) is dominant to rabbit solid coat (r). • A farmer has a spotted coat rabbit. When the rabbit is crossed with a solid coat rabbit, half are spotted and half are solid. • What is the genotype of the spotted rabbit? Show your test cross.

Homework Problems Set #3 • In cattle, red coat crossed with white coat produces roan (pinkish brown). • Cross a red bull with a white cow (show your work). • What percentage will be red? White? Roan?

Homework Problems Set #3 • If a person with type AB blood has children with a person who has type O blood… • Show your work. • What percentage would be type AB? Type O? Type A? Type B?

Homework Problems Set #3 • Hemophilia is a sex linked gene that is carried on the X chromosome exactly like color blindness. • Cross a Normal male with a Normal female who is a carrier. Show your work. • What percentage of offspring would have hemophilia? What percentage of girls have hemophilia? % boys have hemophilia?

Beyond Dominant and Recessive Alleles AND Human Heredity