topic 7:inheritance

Question 1

what are homologous chromosomes?

Answer 1

sperm and egg both contribute a set of chromosomes to offspring
known as homologous pairs because they carry the same genes
but are genetically different because of different alleles

Question 2

total number of chromosomes

Answer 2

46(2n)
diploid

Question 3

number of gametes in sperm and egg cells

Answer 3

haploid (n)
23

Question 4

genotype

Answer 4

the genetic constitution of an organism

Question 5

pheontype

Answer 5

the expression of the genetic constitution and its interaction with the environment

Question 6

allele

Answer 6

a different form of the same gene
codes for a different version of the same characteristic
arise due to random mutations

Question 7

dominant allele

Answer 7

always expressed in the phenotype

Question 8

recessive allel

Answer 8

expressed in the phenotype only in the presence of another identical allele

Question 9

homozygous

Answer 9

if an organism carries 2 identical copies of the same gene
e.g. AA,aa

Question 10

heterozygous

Answer 10

if an individiual possess 2 different copies of the same gene
e.g. Aa

Question 11

how are alleles represented?

Answer 11

using letters
capital letters represent dominant alleles
recessive for the same gene represented by lower case of same letter

Question 12

what is monohybrid inheritance?

Answer 12

the inheritance of a single characteristic (gene) controlled by different alleles

Question 13

ratio of phenotypes in monohybrid inheritance?

Answer 13

3:1 if heterozygotes are crossed

Question 14

what is a Punnett square?

Answer 14

square grid to present results of genetic crosses by showing genotype of offspring
always draw circles round gametes

Question 15

what is dihybrid inheritance?

Answer 15

inheritance of 2 characteristics(genes) controlled by different alleles located on different chromosomes

Question 16

what are dihybrid crosses used for?

Answer 16

to investigate the simultaneous inheritance of 2 different characteristics

Question 17

there is a pattern of offspring produced in dihybrid crosses, as there is in monohybrid inheritance. who first discovered these patterns?

Answer 17

Gregor Mendel in the 19th century
he was a monk famous for carrying out thousands of genetic crosses on pea plants

Question 18

how do you write out the parental gametes in dihybrid inheritance?

Answer 18

one allele from each pair in each gamete
in organisms there are 2 copies of every gene, but the gametes will have one of the copies for every single gene

Question 19

the ration of the F2 generation in any dihybrid cross

Answer 19

9:3:3:1
dominant:gene 1 d, gene 2 r: gene 1 r,gene 2 ;recessive

Question 20

what is a test cross?

Answer 20

a method used to work out the unknown genotypes of individual organisms

Question 21

when is a test cross carried out?

Answer 21

between an individual of unknown genotype showing a dominant phenotype and individual of recessive phenotype

Question 22

what is codominance?

Answer 22

occurs when neither allele for a characteristic is recessive so they are Both expressed

Question 23

what is incomplete or partial codominance?

Answer 23

an intermediate phenotype can be produced in some circumstances when the offspring is heterozygous for both dominant alleles
both are expressed

Question 24

what does it mean to have multiple alleles?

Answer 24

different versions of the same gene on the same locus
more different alleles means more different phenotypes

Question 25

what is sex-linked inheritance?

Answer 25

alleles for sex linked characteristics are located on the sex chromosomes there are 23 pairs of chromosomes,22 are autosomes and the last 2 are the sex chromosomes there are several characteristics coded for by alleles on these the pattern of how these are inherited is sex-linked inheritacne

Question 26

what gametes do females produced

Answer 26

all gametes will have x chromosome

Question 27

what gametes do males produce

Answer 27

one X and one Y half gametes with each

Question 28

why are males more likely than females to show recessive phenotypes for sex linked genes?

Answer 28

males only have one X chromosome so often only have one allele for sex-linked genes because they only have one copy, they express the characteristic of this allele even if its recessive

Question 29

what are X linked conditions?

Answer 29

genetic diseases and conditions caused by faulty alleles located on the X chromosome includes colourblindness and Haemophilia

Question 30

why cant males be carriers of recessive conditions?

Answer 30

they only have one X chromosome so they either have it or don't

Question 31

when will a female be affected by a recessive condition?

Answer 31

if father is a recessive allele, and mother is a carrier of has it herself if mother is affected, all sons will have it and daughters all be carriers

Question 32

what is a pedigree chart?

Answer 32

an alternative method for presenting information about inheritance genetic pedigree diagrams show how an inherited trait runs in a group of related individuals

Question 33

what does a pedigree chart show?

Answer 33

genotypes and phenotypes in different generations gives information on how allele are inherited

Question 34

how do you answer a question including a pedigree chart?

Answer 34

- think of it like a puzzle - work out genotypes you are sure of and write them down next to the individual -this helps to identify patterns between parent and offspring

Question 35

how are females represented in pedigree charts?

Answer 35

circles

Question 36

how are males represented in pedigree charts?

Answer 36

squared

Question 37

how are carriers/heterozygotes represented in pedigree charts?

Answer 37

shape will be half one colour, half other

Question 38

how does a pedigree diagram show a recessive allele

Answer 38

if unaffected parents give rise to an affected individiual

Question 39

what is autosomal linkage

Answer 39

if 2 or more genes are carried on the same autosome autosomes are the remaining 22 chromosomes that arent sex linked

Question 40

what are unlinked genes?

Answer 40

genes located on different chromosomes

Question 41

linkage groups

Answer 41

a set of genes on different loci on the same gene that tend to be inherited together except for crossing over

Question 42

what happens to linked genes in meiosis?

Answer 42

assuming no crossing overall linked genes stay together during meiosis so pass into the gametes and offspring together and don't segregate

Question 43

what happens to genes on different chromosomes?

Answer 43

independent segregation can occur as genes are carried on different pairs of homologous chromosomes

Question 44

what happens if crossing over occurs

Answer 44

variety of gametes increase

Question 45

when is it easier for crossing over to occur?

Answer 45

when genes are far apart on a chromosome

Question 46

when is it harder for crossing over to occur?

Answer 46

when different genes are close to each other

Question 47

what does it mean if chromosomes are recombinant?

Answer 47

any point the genes have switched and have exchanges genetic material

Question 48

why is the chi-squared test used?

Answer 48

to look at the differences between categorical variables in populations basically, what you expect vs what you see

Question 49

what is the null hypothesis?

Answer 49

the opposite of what you expect the experiment to show it is rejected or accepted

Question 50

conclusion from the result of the chi-squared test if it is LESS than the critical value

Answer 50

the chi-squared is less than the critical value which means there is a greater than 5% probability that the results occurred by chance we can accept the null hypothesis there is no significant difference between observed and expected w

Question 51

conclusion from the result of chi squared if it is GREATER than the critical value?

Answer 51

if it is greater than the critical value it means there is a less than 5% probability that results occurred by chance reject null hypothesis there is a significant difference between observed and expected

Question 52

define epistasis

Answer 52

the influence of one gene on the expression of another

Question 53

what does epistasis result in

Answer 53

a combination of genotypes in a hierarchy with each allele more dominant than another leads to a variety of different phenotypes