BSC 2010 Lecture Notes - Lecture 10: Sister Chromatids, Dna Replication, Genetic Linkage

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cyanprairie-dog5

22 Feb 2016

School

University of Florida

Department

Biology - Biological Sciences

Course

BSC 2010

Professor

Chen Sixue

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Mapping and DNA Replication

February 22, 2016

Independent assortment and recombination

oGenes on different chromosomes assort independently

oIf two loci are on different chromosomes half of the gametes will be

parental and half will be recombinant

oThe frequency of recombination is 50% for any two loci on different

chromosomes

Genetic linkage and recombination

oIf sister chromatids break and rejoin, nothing happens

oIf non-sister chromatids rejoin, recombination occurs

oCrossing-over between non-sister chromatids, recombination happens

oOne cross-over produces 2 recombinant chromosomes and leaves 2

parental chromosomes

oThe closer the loci are together, the lower the fraction of recombinant

chromosomes

Linkage mapping

oMapping genes came from the probability of recombination between 2 loci

being the function of the distance between them on the chromosomes

oDouble crossovers

Reduce the apparent distance between the loci

oSample data from loci 6

Linkage groups- groups in which loci are linked (recombination rate

<50%)

May be on different chromosomes or may be far apart on the

same chromosomes

As you add loci to the mapping data on a graph, the number of

linkage groups declines to an asymptote

The asymptote represents the number of chromosomes

oMap units

By convention, one map unit is defined as 1% recombination

frequency

Called a centimorgan

Max recombination frequency is ½

If loci are >50 map units apart they are effectively unlinked

Map distance is not perfectly correlated with numbers of

nucleotides between loci

A map distance of 100 would indicate that the genes are on the

same chromosomes

Historical perspective

oThe state of understanding- 1940

Morgan had clearly established that genes resided on

chromosomes

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Document Summary

Linkage mapping: mapping genes came from the probability of recombination between 2 loci being the function of the distance between them on the chromosomes, double crossovers. Reduce the apparent distance between the loci: sample data from loci 6. Linkage groups- groups in which loci are linked (recombination rate. May be on different chromosomes or may be far apart on the same chromosomes. As you add loci to the mapping data on a graph, the number of linkage groups declines to an asymptote. The asymptote represents the number of chromosomes: map units. By convention, one map unit is defined as 1% recombination frequency. If loci are >50 map units apart they are effectively unlinked. Map distance is not perfectly correlated with numbers of nucleotides between loci. A map distance of 100 would indicate that the genes are on the. Historical perspective same chromosomes: the state of understanding- 1940. Morgan had clearly established that genes resided on chromosomes.

Related Questions

ANSWER ALL the PARTS you can

PART1 Alleles are considered linked if recombination is less than 50% in:

a) a Px P Fl cross

b) an F1 x F1F2 cross

c) an F2 x F2F3 cross

d) an Fl x homozygous recessive cross

e) any F2 progeny x homozygous recessive cross 1.

PART2 If two loci A/a B/b are 9 map units apart, and an Ab/aB individual is testcrossed,

a) There will be 9% AB individuals

b)There will be 91% Ab individuals

c) There will be 4.5% ab individuals

d) There will be 91% recombination individuals

If two genes a and b show 50% recombination genes a and c show 35% recombination, and genes b and show 32% recombination, then

a) Genes a and b are on the same chromosome, and 50 m.u. apart

b) Genes a and b are on different chromosomes

c)Genes a and b are on the same chromosome, and 67 map units apart

d) One cannot tell if genes a and b are on the same or different chromosomes from given data.

PART4 If two genes a and b are 8.3 m.u. a part, one expects to find

a) 8.3% recombinant gametes from a double heterozygous parent

b) 91.7% recombinant gametes from a double heterozygous parent

c) A chiasma between the a and b loci in 8.3% of the meiosis

d) A chiasma between the a and b loci in 91.7% of the meiosis.

PART5 Map distances are most accurate when genes are closely linked because as genes become further apart,

a) They always show independent assortment

b)The chance of multiple crossovers increases

c) They no longer recombine

d) There is chiasma interference

PART6 In a three-point testcross, the most frequent classes of progeny were ABc and abC. The less frequent classes of progeny were AbC and aBc. Which gene is in the middle?

a) Aa

b) B/b

c)C/c

d) It is not possible to tell from just these data

PART7 In a three-point testcross with 100 progeny, there were 16 single crossovers between genes A and B, 29 single crossovers between genes B and C, and 4 double crossovers. The correct gene order was determined to be A-B-C. What is the map distance between A and B?

a) 20%

b) 0.2 m.u

c) 20 m.u.

d) 16 m.u.

e) 29 m.u.

f) 16%

Title: Meiosis Lab

Part 1: Modeling Meiosis Without Crossing Over (reformat as needed)

Take photos of the following stages of your meiosis bead simulation. Insert and label the following images:

Meiosis 1: Prophase I and Metaphase I

Meiosis 2: Metaphase II and Telophase II

Part 2: Modeling Meiosis With Crossing Over (reformat as needed)

Take photos of the following stages of your meiosis bead simulation. Insert and label the following images:

Meiosis with Crossing Over: Metaphase I and Telophase II

Questions â use the lab Introduction, your textbook and other sources to answer the following.

What is the state of DNA at the end of meiosis I? Are the chromosomes replicated or unreplicated? Diploid or haploid?

Why are chromosomes important?

How are Meiosis I and Meiosis II different?

Name two ways meiosis contribute to genetic recombination or genetic variety.

Why do you use non-sister chromatids to demonstrate crossing over? What would happen if you crossed over sister chromatids?

How many chromosomes were present in your simulation when meiosis I started?

Why is it necessary to reduce the chromosome number in gametes, but not in other cells of an organism?

If humans have 46 chromosomes in each of their body cells, determine how many chromosomes you would expect to find in the following:

Sperm	Egg	Daughter cell after mitosis	Daughter cell after meiosis

Investigate a disease that is caused by a chromosomal mutation due to nondisjunction. When does the mutation occur? What chromosome is affected? What are the consequences?

1. What is the chromosome theory of inheritance?

2. Understand how independent assortment can cause gametes to have four combinations of alleles when an individual is heterozygous for two genes on two different chromosomes.

3. What are linked characters and linked genes? Understand why linked genes will not independently assort.

4. How can crossing over affect linked genes?

5. What are recombinant gametes?

6. Define recombinant frequency. Be able to use the recombinant frequency to determine how close two genes are on a chromosome.

7. What is a linkage map?

8. What is the function of the SRY gene on the Y chromosome? What happens if you don't have this gene?

9. Know how sex is determined in mammals, birds, bees and ants, and reptiles.

10. How many autosomes and sex chromosomes do normal human haploid and diploid cells have?

11. What does it mean for a gene to be X-linked or Y-linked?

12. Be able to answer word problems and fill out a Punnet square involving an X-linked recessive trait.