U2T5 - Keywords

Question 1

Gene

Answer 1

Short section of chromosome that codes for particular polypeptide/protein/characteristic.

Question 2

Allele

Answer 2

Particular form of a gene.

Question 3

Homozygous

Answer 3

Both alleles of gene are same. (TT - homozygous dominant, tt - homozygous recessive)

Question 4

Heterozygous

Answer 4

Alleles of same gene are different. (Tt) Effect of recessive allele masked by dominant allele.

Question 5

Genotype

Answer 5

Gene arrangement of alleles to determine particular feature.

Question 6

Phenotype

Answer 6

Outward appearance (tall/short). Results from gene expression + interaction in environment.

Question 7

Gene Locus

Answer 7

Position of gene on chromosome.

Question 8

Haploid

Answer 8

Single set of unpaired chromosomes. e.g. gamete. (n)

Question 9

Diploid

Answer 9

2 complete sets of chromosomes, one from each parent. (2n)

Question 10

n

Answer 10

Number of chromosomes. Humans have 23 pairs so 46 chromosomes.

Question 11

Homologous Chromosomes

Answer 11

2 similar chromosomes that each carry same genes in same locus on chromosome so each cell has 2 copies of each gene.

Question 12

Mendel’s Law of Segregation

Answer 12

The characteristics of an organism are determined by internal factors which occur in pairs. Only 1 of a pair of such factors can be represented in a single gamete.

Question 13

Monohybrid Inheritance

Answer 13

Inheritance of 1 characteristic (round/wrinkled)

Question 14

Backcross/Test Cross

Answer 14

Used to determine unknown genotypes. e.g. can’t know if Tt or TT as same phenotype. Breed plant with homo recessive plant to find out which it is. If homo recessive with hetero, 1:1 ratio. If homo dom with homo recessive, all offspring hetero. Used to confirm pedigree status.

Question 15

Dominant

Answer 15

An allele that will be more likely to be expressed, takes priority over recessive allele. Not more common though e.g. dwarfism is dom but rare.

Question 16

Autosomal

Answer 16

Not carried on sex chromosomes. The other 22 pairs of chromosomes.

Question 17

Autosomal Recessive

Answer 17

Not carried on sex chromosomes, only occurs when you have 2 copies of recessive allele.

Question 18

Heterozygous Advantage

Answer 18

Disease causing alleles which in heterozygous state give selective advantage. e.g. sickle cell anaemia allows resistance to malaria + CF carriers have resistance to typhoid.

Question 19

Codominance

Answer 19

When both alleles are expressed and neither dominates the other. e.g. when red + white flowers bred, pink flowers produced. Uppercase letter used for both alleles. Smaller letter beside it indicates allele type. e.g. RR + WW. Can have partial dominance.

Question 20

Sickle Cell Anaemia

Answer 20

Caused by mutation altering haemoglobin structure. Faulty gene recessive + in homo rec, when o2 partial pressures low in tissues, haemo less soluble + forms crystals in cell, resulting in sickle shaped cells which can stick in narrow blood vessels causing blockage + o2 starvation. Results in early death (anaemia as lots of RBCs destroyed). Most common in Africans where malaria incidence high. If hetero, gen health good as only 40% haemo affected. Suffer mild anaemia normally but have malaria resistance.. More common in malarial places.

Question 21

Lethal Allele Combinations

Answer 21

Abnormal ratios in offspring. e.g. sickle cell anaemia combo of 2 recessive alleles lethal. If breed 2 yellow mice, don’t get all yellow offspring. Expected ratio is 3:1 but in reality, doesn’t happen. In yellow pairs, female has dead embryos in uterus whilst if yellow + grey, few if any found. All yellow mice hetero + carry grey allele.

Question 22

Dihybrid Inheritance

Answer 22

Inheritance of 2 characteristics. When genes on sep chromosomes, they’re unlinked.

Question 23

Mendel’s Law of Independent Assortment

Answer 23

Each member of an allelic pair may combine randomly with either of another pair.

Question 24

Multiple Alleles

Answer 24

Genes have more than 2 alleles that can occupy the gene locus on a pair of homologous chromosomes at any one time in any individual.

Question 25

Homogametic

Answer 25

Females. Only produce one type of gamete, all with X.

Question 26

Heterogametic

Answer 26

Males. Produce 2 types of gametes, half with X, half with Y. Means 50% chance of either sex at fertilisation.

Question 27

Sex-Linked Characteristics

Answer 27

Refers to genes carried on sex chromosomes. Mainly carried on X chromosome. Hairy ears determined by sex-linked allele on Y chromosome so sons always inherit from them.

Question 28

Polygenic Character

Answer 28

Single characteristic controlled by alleles of 2 or more genes that interact with each other. Transmitted by polygenic inheritance.

Question 29

Polygenic Inheritance

Answer 29

The way a polygenic character is transmitted through the generations. Basis of continuous variation.

Question 30

Continuous Variation

Answer 30

Character shows range of phenotypes with smooth graduation from one extreme to another. Many characters are polygenic. Multiple alleles could account for this but would need lots. Diff as multiple alleles at same locus + polygenic on several loci.

Question 31

Hermaphrodite

Answer 31

Xxy

Non segregation of sex chromosomes during meiosis.

Question 32

Haemophilia

Answer 32

Caused by recessive gene mutation which prevents formation of protein involved in blood clotting, leads to prolonged bleeding in those affected.

Question 33

Discontinuous Variation

Answer 33

Mendel used characters to show this. Form discrete groups of characteristics, rather than continuous variation. Pea plant height discontinuous so only one gene involved.

Question 34

Epistasis

Answer 34

1 gene modifies/masks action of another gene. 2 diff genes both affect same characteristic, can give rise to unusual ratios in genetic crosses. These genes at diff loci.

Question 35

Chi-squared test

Answer 35

To find out if offspring characteristic nums fit expected ratio. Statistical test used when data consists of discrete variables. Compares observed with expected. Diff is deviation from expected. If significant deviation, not due to chance alone. Null Hypothesis used.

Question 36

Null Hypothesis

Answer 36

Observed frequencies compared with expected frequencies based on this during chi-squared test. Prediction that assumes no signif diff between observed + expected ratios. Normally stated at start of stat test which it then proves or disproves.

Question 37

Degrees of freedom

Answer 37

Need value for this to know where to read probability table. If monohybrid cross, will be 2 classes. Calculated by counting num of classes + subtracting 1 from this total so there is 1 in this case. If dihybrid, 4 classes so 3 degrees. Prob table then read at row corresponding to num of degrees of freedom to where X2 num fits.

Question 38

Gene Interaction

Answer 38

Interaction between multiple genes that impacts phenotype.

Question 39

Agouti

Answer 39

Greyish pattern formed on mice by bands of alternating pigment in each hair.

Question 40

Genetics

Answer 40

Science of heredity, now characteristics pass throughout the generations.

Question 41

Gregor Mendel

Answer 41

Started the study of genetics with his experiments on pea plants. Was a monk in Czech Republic. Studied inheritance of characteristics.

Question 42

Pure Breeding

Answer 42

Homozygous for a particular trait.

Question 43

Progeny

Answer 43

Offspring

Question 44

Recessive

Answer 44

Dominated by dominant allele. Only shows in phenotype if there are 2 recessive alleles for the particular trait.

Question 45

Pedigree Charts

Answer 45

Used to show inheritance of trait through generations. Males are squares. Females are circles. Shading indicates the occurrence of the trait being studied.

Question 46

Huntington’s Disease

Answer 46

Autosomal dominant so can’t skip a generation.

Question 47

Autosomal Dominant

Answer 47

Can’t pass on condition without at least one person having trait. Both males and females get it.

Question 48

X-linked recessive

Answer 48

More common in males.

Question 49

X-linked Dominant

Answer 49

Affects both males and females equally.