crosses incomplete dominance, codominance, blood types, sex-linkage - - PowerPoint PPT Presentation

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crosses incomplete dominance, codominance, blood types, sex-linkage - - PowerPoint PPT Presentation

Mar 19, 2023 203 likes •759 views

Use Punnett squares for unusual monohybrid crosses incomplete dominance, codominance, blood types, sex-linkage Use Punnett square for dihybrid crosses VOCABULARY Incomplete dominance Pleiotropy Codominance Sex-linked

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▪Use Punnett squares for unusual monohybrid

crosses – incomplete dominance, codominance, blood types, sex-linkage

▪Use Punnett square for dihybrid crosses

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VOCABULARY

▪Incomplete dominance ▪Codominance ▪Polygenic trait ▪Epistasis ▪Multiple alleles ▪Pleiotropy ▪Sex-linked trait ▪Barr body ▪Gene mapping ▪Gene linkage

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TRAIT

▪Ways of looking, thinking, or being ▪Types of traits

▪Dominant (Topic 1) ▪Recessive (Topic 1) ▪Polygenic (Topic 2) ▪Sex-linked (Topic 2) ▪Autosomal (Topic 3)

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COMPLETE DOMINANCE

▪In Mendel’s classic pea crosses, the F1 offspring always

looked like one of the two parental varieties because one allele in a pair showed complete dominance

▪Phenotypes of heterozygote and dominant homozygote are

indistinguishable

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+ =

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INCOMPLETE DOMINANCE

▪There is no dominant allele or recessive allele ▪Example: Red (RR) x White (rr) = Pink (Rr)

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CODOMINANCE

▪There is no dominant allele or recessive allele but

both are expressed

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PRACTICE

If brown hair and white hair horse alleles show incomplete dominance, what offspring ratios will you see if you cross a brown horse with a white horse?

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If red and white flower alleles show codominance, what

  • ffspring ratios will you see if

you cross a red flower with a white flower?

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▪Use Punnett squares for unusual monohybrid

crosses – incomplete dominance✔, codominance✔, blood types, sex-linkage

▪Use Punnett square for dihybrid crosses

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POLYGENIC TRAIT

▪Two or more genes affect a single phenotype ▪Example: Eye color, skin color, height

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EPISTASIS

▪The phenotypic expression of one gene alters that

  • f another independently inherited gene

▪Example: Coat color in Labrador retrievers

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MULTIPLE ALLELES

▪ Two or more alleles

affect a single gene

▪ Example: Blood type

(A, B, O)

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PRACTICE

If a father with blood type A (IAi) and mother with blood type B (IBi) have a child together, what

  • ffspring ratios will you see?
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PLEIOTROPY

▪A single gene has multiple effects on unrelated traits ▪Example: Sickle cell anemia

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COMPARE AND CONTRAST

Polygenic trait Multiple alleles Pleiotropy

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SEX-LINKED TRAIT

▪A gene is located on either sex chromosome ▪Most are found on the X chromosome ▪Example: Hemophilia (x-linked) causes blood not to

clot, Auricular hypertrichosis (y-linked) which causes excessive hair in the ear

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THOMAS MORGAN

▪Early 1900s, he and his students studied a species

  • f fruit flies, Drosophila melanogaster

▪Discovered sex-linked traits by choosing the right

experimental organism for his research

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THOMAS MORGAN

▪“Two years’ work wasted. I have been breeding

those flies for all that time and I’ve got nothing out

  • f it.”

▪Eventually, he and his team discovered a mutant

male with white eyes (Xr)

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▪Fruit flies have only four pairs of

chromosomes (three pairs of autosomes, one pair of sex chromosomes)

▪Prolific breeders with hundreds of

  • ffspring from each mating

▪New generation every two weeks

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PRACTICE

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PRACTICE

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SHARE

For the next minute, quietly think about the following questions. For the next minute, with your neighbor, talk about your responses.

Question:Why are males affected much more often than females by X-linked disorders?

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BARR BODY

▪An inactivated X chromosome in each cell of a female

mammal

▪Example: Tortoiseshell cats have both cells where the X

chromosome with orange allele is active and cells where the X chromosome with black allele is active

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PICK

▪For the next 15 minutes, quietly work alone or with your

neighbor to create a question a genetics problem to be given as an assignment to a classmate.

▪The problem must test incomplete dominance,

codominance, multiple alleles, polygenic traits, or sex- linked traits.

▪Your problem must have an answer key that includes all

  • f your work.
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✓Use Punnett squares for unusual monohybrid

crosses – incomplete dominance, codominance, blood types, sex-linkage

▪Use Punnett square for dihybrid crosses

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GENE MAPPING

▪Determining the precise position of a gene on a

chromosome

▪Once the position is known, it can be shown on a

diagram

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GENE LINKAGE

The tendency of DNA sequences that are close together on a chromosome to be inherited together during meiosis

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Mendel’s F1 Generation Self- or cross-pollination

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PRACTICE

If you have a grey bodied, striped fish (GgRr) breed with a yellow bodied, unstriped fish (ggrr), how would you write that on a dihybrid cross and what would the phenotype ratios be?

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GgRr x ggrr