Lecture 10 - How Are Genes Organised on Chromosomes?

Question 1

What is an allele?

Answer 1

different versions of the same gene

Question 2

What is the genotype?

Answer 2

the alleles that you have

Question 3

What is your phenotype?

Answer 3

your appearance

Question 4

What are Mendel’s concepts?

Answer 4

1) alternative alleles account for variations in inherited characteristics
2) for each character an organism inherits two alleles one from each parent
3) if two alleles at a locus differ then one (the dominant one) determines the organisms appearance. The recessive one doesn’t affect appearance
4) two alleles for each character separate during gamete formation - the law of segregation

Question 5

What does wild type mean?

Answer 5

the predominant allele / variant

Question 6

What is a mutant gene?

Answer 6

any other form of gene that is distinct from the wild type

Question 7

What do P and F mean in a monohybrid cross?

Answer 7

P = parental
F = filial

Question 8

Explain sex linked inheritance

Answer 8

• In males where they have a Y chromosome that is shorter than the X there will only be one copy of alleles on the X chromosome
• This will mean that the only allele present will be expressed

Question 9

What is genetic linkage?

Answer 9

When genes are located close to each other on the chromosome and they tend to be inherited together

Question 10

What is a test cross?

Answer 10

Determining the genotype of a dominant individual by crossing it with a recessive individual

Question 11

What will be the ratio of traits if they are on different chromosomes?

Answer 11

1 : 1 : 1 : 1

Question 12

What will be the ratio of traits if they are on the same chromosome?

Answer 12

1 : 1 : 0 : 0

Question 13

Why will you sometimes see some recombination in traits that are on the same chromosome?

Answer 13

rare recombination events between the two alleles

Question 14

How do you calculate recombination frequency?

Answer 14

= (recombinants / total offspring) x 100

Question 15

What is a centimorgan?

Answer 15

the difference between two loci

Question 16

What is abnormal chromosome numbers called?

Answer 16

aneuploidy

Question 17

What is a monosomy mutation?

Answer 17

one missing chromosome (2n - 1) - monosomic

Question 18

What is a trisomy mutation?

Answer 18

one extra chromosome in the zygote (2n + 1) - trisomic

Question 19

What is a polyploidy mutation?

Answer 19

extra full sets of chromosomes
- triploid = 3n
- tetraploid = 4n

Question 20

What are 4 mutations in chromosome structure?

Answer 20

• deletion
• duplication
• inversion
• translocation

Question 21

What is a deletion mutation?

Answer 21

loss of chromosome fragment

Question 22

What is a duplication mutation?

Answer 22

addition of a broken fragment resulting in repetition of genetic information

Question 23

What is an inversion mutation?

Answer 23

re-addition of a broken fragment but in wrong orientation

Question 24

What is a translocation mutation?

Answer 24

movement of part of a chromosome onto a different chromosome

Question 25

What is mis-segregation?

Answer 25

non-disjunction - either homologous chromosomes or sister chromosomes don’t separate when being pulled by spindles, both go to the same pole

Question 26

When can mis-segregation happen?

Answer 26

meiosis I or II