Linkage and chromosomes

Question 1

Law of separation?

Answer 1

Anaphase 1 - separation of homologs accounts for the segregation of the 2 alleles of a gene into seperate gametes

Question 2

Law of independent assortment?

Answer 2

Metaphase 1 - A random arrangement of chromosome pairs accounts for independent assortment of alleles for 2 or more genes located on different homolog pairs.

Question 3

Hemizygous?

Answer 3

Men have only 1 locus for a X-allele

Question 4

X-inactivation?

Answer 4

The X-chromosome becomes inactivated forming a Barr body and females consists of a mosaic of 2 types of cells - active from father and active from mother - all mitotic descendants of that cell will recieve the same Barr body and one XIST.

Question 5

Linked genes?

Answer 5

Genes located near each other on the same chromosome tend to be inherited together in genetic crosses.

2 or more genes on the same chromosome that tend to be inherited together.

Question 6

Sex-linked genes?

Answer 6

Single gene on a sex chromosome

Question 7

Non-parental phenotypes?

Answer 7

Combinations of traits not seen in P-generation

Question 8

Genetic recombination?

Answer 8

Production of offspring with combinations of traits that differ from the P-generation.

Sexually reproductive offspring -

Independent assortment of chromosomes
Crossing over
Possibility of any sperm fertilizing an egg

Question 9

Recombination of unlinked genes?

Answer 9

Combinations of traits that do not match the P-generation. A 50% RF is obeserved for any 2 genes that are located on different chromosomes and cannot be linked because of the independent assortment of the 2 unlinked genes during meiosis.

Question 10

Recombination of linked genes?

Answer 10

Occurence of parental types with a RF of less than 50% = genes are linked.

The effect comes from crossing over in the prophase 1 where corresponding segments of 1 maternal and 1 paternal chromatid

Question 11

A single crossover?

Answer 11

End portions of 2 non-sister chromatids trades place.

Question 12

RF?

Answer 12

Recombinants / Total offspring x 100 = %

Reflects combinations of alleles not seen before in either P-generation.

Question 13

Genetic map?

Answer 13

An ordered list of the genetic loci along a chromosome

Question 14

RF and Mapping?

Answer 14

The D between genes on chromosomes - the farther apart 2 genes are the higher the probability that a crossover will occur between them = higher RF

The longer D between 2 genes the more points there are between them where crossing over can occur

Because if they are close = they would follow during a crossover since 2 segments exchange between 1 paternal and 1 maternal.

Question 15

Linkage map?

Answer 15

A genetic map based on RF 1 mu = 1% and gives a good approximation since it is only based on RF and can portray an order of genes along a chromosome but not precisely the the loci of genes.

Question 16

Non-disjunction?

Answer 16

Members of a pair of homologs do not move apart during meiosis or sister chromatids fail to separate.

1 gamete recieves 2 of the same chromosome and 1 no copy.

Question 17

Aneuploidy?

Answer 17

Abnormal number of chromosomes.

Monosomic or trisomic

Question 18

Polyploidy?

Answer 18

2 or more complete chromosomes in somatic cells.

Triploidy - 3n = 3 sets
Tetraploidy - 4n = 4 sets

Question 19

Alternations of chromosome structure?

Answer 19

Errors in meiosis can cause breakage of chromosomes

Question 20

Deletion?

Answer 20

Chromosomal fragment is lost

Question 21

Duplication?

Answer 21

The deleted segment may become attached as an extra segment to a sister chromatid or non-sister chromatid

Question 22

Inversion?

Answer 22

A fragment can reattach to the original chromosome but in reverse orientation

Question 23

Translocation?

Answer 23

A fragment joins a non-homologous chromosome

Question 24

Deletion and duplication?

Answer 24

Likely to happen during meiosis

Crossing between non-sister chromatids that exchange unequal sized segments of DNA = 1 partner recieves more than it recieves

Question 25

Genomic imprinting?

Answer 25

Variation in phenotype depends on if the allele is inherited from male or female parent.

A mechanism that silences or activates a allele of a certain gene during gamete formation, and transmitted to all body cells during the development.

Question 26

Cytoplasmic genes?

Answer 26

Mitochondria from the cytoplasm of the egg and mutations gradually accumulate in the mitochondria.