standard 2.2 molecular basis of inheritance a sorting and recombination of genes during sexual...

Standard 2.2 Molecular basis of inheritance

A sorting and recombination of genes during sexual reproduction results in a great variety of possible gene combinations from the offspring of any two parents (i.e.,

Punnett squares and pedigrees). Students will understand concepts in a single trait cross (e.g., alleles, dominant trait, recessive trait, phenotype, genotype,

homozygous, heterozygous, incomplete dominance, and sex-linked traits).

The rule of dominance

• An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele.

• The dominant allele is always written first…rule of ?

T T

T

T

t t

t

tAll tall plants

F1

Tall plant Short plant

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3

4

5

• A Punnett square for this cross is two boxes tall and two boxes wide because each parent can produce two kinds of gametes for this trait.

Monohybrid crosses

Heterozygous tall parent

T t

T t

T t

T

t

Heterozygous tall parent

T t

T

t

TT Tt

Tt tt

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1:4 or 25% and millimeters is length while grams is measuring mass

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17.In a certain group of lab mice black fur is dominant and brown fur is recessive. If two heterozygous mice mate and produce 16 offspring, how many of the offspring will probably have brown fur?

A 0B 4C 8D 12

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• Incomplete Dominance• appearance of a 3rd

phenotype.

• Example: A homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (R’R’), all of the F1 generation offspring will have PINK flowers (RR’).

RR’ RR’

RR’ RR’

R R

R’

R’

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• Codominance • Expression of both alleles

• Example: Black (BB) rooster crossed with a white (WW) hen = checkered (BW) black and white. (Incomplete dominance would have been gray!)

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• The 23rd pair of chromosomes in humans are ___ ____________and determine the sex of the offspring.

XX = femaleXY = male

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sex chromosomes

• Traits controlled by genes located on sex chromosomes

• sex-linked traits

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• Traits controlled by more than 2 alleles have this…

• multiple alleles

• Example: Pigeons have 3 alleles that control feather color.

• BA = ash red • B = blue • b = chocolate

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• Polygenic inheritance• pattern of a trait that is

controlled by 2 or more genes.

• Example: eye color, skin color, height (AaBbCc…)

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• Pedigree• graphic of genetic inheritance

= Male

= Female

= affected Male

= affected Female

= Mating

= Parents

= Siblings

= known heterozygous “carriers”

= Death

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