genetics & inheritance

Question 1

definition of a gamete?

Answer 1

sex cells

Question 2

definition of a chromosome?

Answer 2

thread like structures of DNA, carrying genetic information in the form of genes. located in nucleus of the cell

Question 3

definition of a gene?

Answer 3

a section of DNA found on chromosomes that codes for a specific protein/a trait

Question 4

definition of an allele?

Answer 4

different versions/variations of a particular gene

Question 5

definition of a dominant allele?

Answer 5

an allele that’s always expressed, even if only one copy is present

Question 6

definition of a recessive allele?

Answer 6

an allele that’s only expressed if two copies are present (therefore no dominant allele present)

Question 7

definition of homozygous?

Answer 7

if the two alleles of a gene are the same

Question 8

definition of heterozygous?

Answer 8

if the two alleles of a gene are different

Question 9

definition of a genotype?

Answer 9

the combination of alleles that control each characteristic

Question 10

definition of a phenotype?

Answer 10

the observable characteristics of an organism, or the genotype that is expressed

Question 11

true or false: some characteristics are controlled by a single gene

Answer 11

true, the inheritance of these single genes is monohybrid inheritance

Question 12

what’s an example of monohybrid inheritance?

Answer 12

fur colour in mice, red-green colour blindness in humans

Question 13

do we have two alleles for each gene, and why?

Answer 13

• yes
• 2 copies of each chromosome, 2 copies of each gene, therefore 2 alleles for each gene
• 1 of the alleles inherited from mother, other from father

Question 14

a dominant allele needs to be inherited from ___ parent in order for the characteristic to show up in the phenotype

Answer 14

a dominant allele needs to be inherited from one parent in order for the characteristic to show up in the phenotype

Question 15

a recessive allele needs to be inherited from ____ parents in order for the characteristic to show up in the phenotype

Answer 15

a recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype

Question 16

what do homozygous dominant and homozygous recessive mean?

Answer 16

homozygous dominant: having two copies of the dominant allele

homozygous recessive: having two copies of the recessive allele

Question 17

what letters are given to dominant and recessive alleles when completing genetic diagrams?

Answer 17

dominant: capital letter
recessive: same letter but lower case

Question 18

what does polygenic mean?

Answer 18

characteristics that are controlled by more than one gene

(most characteristics are a result of multiple genes interacting, rather than a single gene)

Question 19

what can the phenotypes of polygenic characteristic show?

Answer 19

a wide range of combinations in features

Question 20

what does polygenic inheritance mean?

Answer 20

the inheritance of polygenic characteristics

Question 21

why do we not usually use genetic diagrams for polygenic inheritance?

Answer 21

because it’s difficult to show due to the wide range of combinations

e.g. eye colour: while it’s true brown eyes dominant to blue eyes, not as simple as this as eye colour’s controlled by several genes. this means there’s several different phenotypes beyond brown & blue, like green & hazel

Question 22

how can the inheritance of characteristics be determined?

Answer 22

using Punnet squares

Question 23

what do punnet squares show?

Answer 23

the possible combinations of alleles that could be produced in the offspring

Question 24

what do F1 and F2 mean?

Answer 24

first generation and second generation

Question 25

what are family tree diagrams/pedigrees usually used for?

Answer 25

to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family

—> this can be used to work out probability that some1 in family will inherit the genetic disorder

Question 26

what is codominance?

Answer 26

• when two alleles cross that are both dominant
• when this happens the organism may show multiple phenotypes

Question 27

how do you represent codominance on a punnet square?

Answer 27

use same capital letter for each allele & add another letter to top right-hand corner to represent their differences
—> both alleles are dominant, therefore both need 2 be represented by capital letter