Top Banner
Dihybrid Crosses What are the four possible gametes that the individuals with these genotypes could produce? (Remember to keep the genes in this order, so I/i before L/l, F/f before J/j, etc.) – IiLL – iiLL – FFjj – ffJJ – YyHh
27

Dihybrid Crosses

Feb 06, 2016

Download

Documents

Zander_

Dihybrid Crosses. What are the four possible gametes that the individuals with these genotypes could produce? (Remember to keep the genes in this order, so I/i before L/l, F/f before J/j, etc.) IiLL iiLL FFjj ffJJ YyHh. Dihybrid Crosses. Homework. Objectives. - PowerPoint PPT Presentation
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Dihybrid Crosses

Dihybrid Crosses

What are the four possible gametes that the individuals with these genotypes could produce? (Remember to keep the genes in this order, so I/i before L/l, F/f before J/j, etc.)

– IiLL– iiLL– FFjj– ffJJ– YyHh

Page 2: Dihybrid Crosses

Dihybrid Crosses

Page 3: Dihybrid Crosses

Homework

Page 4: Dihybrid Crosses

Objectives

Be able to perform a dihybrid cross– Be able to identify what each box in the

cross represents– Be able to explain what Mendel’s three

Laws are, and where you can see each one “in action” in a dihybrid cross

Page 5: Dihybrid Crosses

Dihybrid Crosses

Popcorn reading: The first two pages of the handout, telling the story of the Morgan fruit fly experiments.

Page 6: Dihybrid Crosses

Gregor Mendel

All of these basic principles were first identified by Gregor Mendel, an Austrian monk in the mid-1800s.– Through studying pea

plant breeding, he described three laws of inheritance.

QuickTime™ and a decompressor

are needed to see this picture.

Page 7: Dihybrid Crosses

Mendel’s Laws of Inheritance

Law of Dominance: In a cross of parents that are pure (homozygous) for contrasting traits, offspring will only have one of those traits.– What is this describing that you’ve already

learned?– Could you rephrase it to make more sense

to you?

Page 8: Dihybrid Crosses

Mendel’s Laws of Inheritance

Law of Segregation: A parent’s allele pair separates during gamete formation, and alleles randomly unite in fertilization.– Let’s figure out how we actually already

learned this when we studied meiosis…

Page 9: Dihybrid Crosses

Mendel’s Laws of Inheritance

Law of Independent Assortment: Alleles of different genes separate independently during gamete formation. Therefore, traits pass to offspring independently of each other.– Again, let’s think back to meiosis, the

candy lab, the Baby Lab…

Page 10: Dihybrid Crosses

Laws Law of Segregation: A parent’s allele pair separates

during gamete formation, and alleles randomly unite in fertilization.– = Each gamete contains only one of each kind of allele.

Law of Independent Assortment: Alleles of different genes separate independently during gamete formation. Therefore, traits pass to offspring independently of each other.– = The parent makes an equal number of each of the four kind of

gametes. A gamete with an allele from one gene does not force it to have a certain allele from the other gene.

• For instance, for a parent who is BbHh, half their gametes have the H allele. Half of those will have the B allele, and the other half will have the b allele. The B/b alleles assorted independently of H. If they had been dependent, then it could be that gametes with H would only have b.

Page 11: Dihybrid Crosses

Dihybrid Crosses

So you know how to figure out the likelihood of having a blue-eyed baby. And you know how to figure out the likelihood of having a baby with a hitchhiker’s thumb.– But what if you want to know the likelihood of

having a brown-eyed baby with a hitchhiker’s thumb?

– A blue-eyed baby with a normal thumb?

Page 12: Dihybrid Crosses

Dihybrid Cross

For two genes that are on different chromosomes, we can do a dihybrid cross. (Di=two) – (Scientists can do very large complicated crosses,

but two is the largest one we’ll do.)

The essential difference is that figuring out gametes has a bit of a trick to it.– Baby Lab, the sequel!

Page 13: Dihybrid Crosses

Dihybrid Crosses Suppose that a person is heterozygous for eye color

(Bb). On one chromosome #1, they have the B allele. On the other chromosome #1, they have the b allele.– Write B on one strip, and b on another.– Write #1 at the top of both, just like in the baby lab.

This person is also heterozygous for hitchhiker’s thumb.– Write H on the third strip, and h on the fourth.– Write #2 at the top of both, just like in the baby lab.

These are their chromosomes in a diploid cell.

Page 14: Dihybrid Crosses

Dihybrid Crosses

When they make gametes, each gamete will get just one from each pair of homologous chromosomes.– Make different gametes. Each gamete should

have just one B/b chromosome, and just one H/h chromosome. Be prepared to answer:

• How many possible combinations are there?• What are the genotypes of those possible alleles?

Page 15: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

A gamete from a person who is Bb will have either B or b. And a gamete from a person who is Hh will have either H or h. This is the same situation.

Page 16: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

BH

Page 17: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

BH Bh

Page 18: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

BH Bh bH

Page 19: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

BH Bh bH bh

Of the four gametes, what % have B? b? H? h?

Page 20: Dihybrid Crosses

Dihybrid Crosses

This person’s genotype is B b H h

BH Bh bH bh

We keep the genes in the same order, regardless of capitalization, like they’re a first and last name.

Page 21: Dihybrid Crosses

Dihybrid Crosses

Everyone get a whiteboard…

What are the gametes that can be made from: JJYy– Note, some gametes may be the same as

each other. Write all four of them anyways.

Page 22: Dihybrid Crosses

Dihybrid Crosses

JJYy = – JY JY JY Jy

Another practice problem, figure out the four gametes for:– ttGg

Page 23: Dihybrid Crosses

Dihybrid Crosses

ttGg = – tG tG tG tg

You set a dihybrid cross up exactly like a monohybrid cross, only now there are four gametes per parent rather than just two.

Example: A cross between IiLL and iill.– Let’s find genotype and phenotype ratios &

probabilities

Page 24: Dihybrid Crosses

Dihybrid Cross

Try this cross, find genotype and phenotype ratios & probabilities.

FFjj x ffJJ

Page 25: Dihybrid Crosses

Dihybrid Cross

Now try this cross: YyHh x YyHh.

Y = jagged, y = normal. H = square, h = round.

Find genotype and phenotype ratios & probabilities. (Helpful hint: 1/16 = 6.25%, 2/16 = 12.5%.)

Page 26: Dihybrid Crosses
Page 27: Dihybrid Crosses

• YyHh x YyHh.

• Genotype Probabilities: 6.25% YYHH, 12.5% YYHh, 12.5% YyHH, 25% YyHh, 6.25% YYhh, 12.5% Yyhh, 6.25% yyHH, 12.5% yyHh, 6.25% yyhh

• Genotype Ratios: 1 YYHH : 2 YYHh : 2 YyHH : 4 YyHh : 1 YYhh : 2 Yyhh : 1 yyHH : 2 yyHh : 1 yyhh

• Phenotype Probabilities: 56.25% jagged/square, 18.75% jagged/round, 18.75% normal/square, 6.25% normal/round

• Phenotype Ratios: 9 jagged/square : 3 jagged/round : 3 normal/square : 1 normal/round

YH Yh yH yh

YH YYHH YYHh YyHH YyHh

Yh YYHh YYhh YyHh Yyhh

yH YyHH YyHh yyHH yyHh

yh YyHh Yyhh yyHh yyhh