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Crosses and Chromosomes. Do Now ( dihybrid cross) In fruit flies, red eyes are dominant to white, and wings are dominant to no wings Draw a Punnett square representing a cross between two flies heterozygous for both traits. What is the probability of having a white-eyed wingless offspring? .

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crosses and chromosomes

Crosses and Chromosomes

Do Now (dihybrid cross)

In fruit flies, red eyes are dominant to white, and wings are dominant to no wings

Draw a Punnett square representing a cross between two flies heterozygous for both traits.

What is the probability of having a white-eyed wingless offspring?

quiz review
Quiz Review
  • 1: floppy completely dominant to pointy
  • 2: yellow + orange = codominant
  • 3: more common in men = sex-linkage
  • 4: in between phenotype (blend) = incomplete dominance
  • 5: 4 phenotypes = >2 alleles
6 sex linkage
6: Sex-Linkage

Carrier f.

50% of males will be colorblind

50% of females will be colorblind, 50% will be carriers.

No females w/ disease

Normal m.

7 multiple alleles
7: multiple alleles

Green + Blue

1:1 green spots:blue

OO = no spots

No spots

dihybrid punnett square
Dihybrid Punnett Square

PY Py pY py

PY Py pY py

test wednesday
TEST WEDNESDAY
  • COME TO COACH CLASS TOMORROW!
  • TOPICS:
    • Chromosomes, cell reproduction, crosses, + today’s topics (Mendel’s Laws + crossing over)
  • CHAPTER 9
mendel s law of segregation
Mendel’s Law of Segregation
  • A pair of factors is segregated (separated) during the formation of gametes (sex cells)

Y

y

For example:

50%

Of Gametes

50%

Of Gametes

slide9

Mendel’s Law of Independent Assortment

  • Factors (alleles) for different characteristics are distributed independently from one another.

T

T

t

t

Y

Y

y

y

For example:

25%

Of Gametes

25%

Of Gametes

25%

Of Gametes

25%

Of Gametes

mendel s laws of heredity
Mendel’s “Laws” of Heredity
  • It is important to note that these “laws” work under certain conditions:
    • Each gene is on a different chromosome
    • The organisms are diploid
it s all about the chromosomes
It’s all about the Chromosomes

b

B

  • In meiosis, the chromosome number is reduced by half (2nn; diploidhaploid)
  • 50% of gametes get one allele, 50% get the other.

b

b

B

B

dihybrid gametes
Dihybrid Gametes
  • Pea plant cross: PpYy x PpYy
  • Gametes: reproductive haploid cells (sperm and egg)
  • One individual heterozygous for 2 traits can produce 4 (2n, where n= number of different genes)possible combinations of alleles.
  • PY
  • Py
  • pY
  • py
dihybrid punnett square1
Dihybrid Punnett Square

PY Py pY py

PY Py pY py

one more twist
One More Twist

a

A

  • crossing over: when two homologous chromosomes exchange material during meiosis, leading to a new combination of alleles

B

b

a

A

B

b

meiosis and genetics
Meiosis and Genetics
  • The 2 alleles a diploid organism has for a trait are located on 2 homologous chromosomes.
  • The separation of these chromosomes during meiosis leads to the 50/50 chance of a gamete having one version or the other.
  • Mendel’s Laws of heredity only work for alleles on different chromosomes.
  • Crossing over creates new combinations of alleles.