Genes And Patterns Of Inheritance

Question 1

Gene

Answer 1

Length of DNA that codes for a particular trait

Question 2

Genetic Locus

Answer 2

Position of gene on the chromosome

Question 3

Allele

Answer 3

Alternative forms for each gene

Question 4

What do chromosomes exist as

Answer 4

Homologous Pairs
Homologous chromosomes have same genetic loci

Question 5

Homozygous Individual

Answer 5

Alleles on homologous chromosome are the same

Question 6

Heterozygous Individual

Answer 6

Alleles on the homologous chromosomes are different

Question 7

Genotype

Answer 7

Represented by two alleles for a particular trait

Question 8

Phenotype

Answer 8

Actual appearance of the trait

Question 9

How may a phenotype be modified

Answer 9

Alleles of other genes
Environmental factors

Question 10

Dominant Allele

Answer 10

Has its instruction followed
Its effect is produced in heterozygous condition

Question 11

Recessive Allele

Answer 11

Allele that does not have its instruction followed in heterozygous condition

Question 12

Heredity

Answer 12

Transfer of genetic factors from one generation to the next

Question 13

Monohybrid Inheritence

Answer 13

Inheritance of the alleles of a single gene

Question 14

Mendels First Law

Answer 14

When any individual produces gametes, the alleles separate, so that each gamete receives only one allele of

Question 15

Sexual Reproduction

Answer 15

Zygote produced from fusion of male and female gametes

Gametes are haploid - only contain one allele of each gene

While a person has a pair of alleles for any genetic condition - only one allele of pair is passed on via any one gamete

Question 16

Analysis of Patterns Inheritance Phenomena

Answer 16

•alleles separated in production of gametes
•alleles combine at fertilisation when gametes fuse

Question 17

Different Patterns of Inheritance provided by

Answer 17

•Dominance - heterozygote same phenotype as homozygous dominant

•Codominance - interaction of alleles results in a hetero with its own distinctive phenotype

•Lethal Allelic Combinations - one allele in homozygous state causes death at early stage

•Multiple Alleles - more than 2 alleles of gene available

•Sex linkage - gene located on sex chromosome - most often X

Question 18

Dominance

Answer 18

Gregor Mendel experiments on pea plants - bred plants through 2 generations and in large no. so ratios reliable

Cross purple flower and white flower - First gen purple but when interbred with 2nd filial gen was mixture of purp and white ratio 3:1

PP purple
Pp purple
pp white

Question 19

Test cross

Question 20

Codominance

Answer 20

Heterozygote phenotype distinctive from homozygotes

Snapdragon
Cr = red
Cw = white

Cr Cr = red
Cr Cw = pink
Cw Cw = white

Question 21

Lethal Allelic Combinations

Answer 21

Many alleles code for essential proteins - absence of proteins prevents operations of vital functions

Most recessive so only homozygous

Question 22

Types of Lethality

Answer 22

•early embryonic stage
•after reduced lifespan
•early stage of development

Question 23

Lethality in early embryonic stage

Answer 23

No obvious evidence that the lethal allelic combination ever occurrd

Question 24

Lethality after reduced lifespan

Answer 24

Tay-Sachs disorder of CNS caused by absence of hexosaminidase - lipid GM2 ganglioside accumulates abnormally in cells - particularly nerves of brain

Ongoing accumulation results in progressive damage to nerve cells - death occurs early childhood

Question 25

Lethality at early stage of development

Answer 25

Presence evident in heterozygote where it displays a distinctive phenotype E.g. yellow coat in mouse. A code for prod of signalling protein - prod agouti colour - associated with proper embryo dev Ay fails to code for protein and associated with obesity, diabetes and cancer - yellow coat from failure to prod black pigment AyAy lethal since lacks proper embryonic dev AA agouti AAy yellow AyAy death Not incl in ratio

Question 26

Multiple Alleles Blood

Answer 26

Ia prod Antigen A Ib prod antigen B Io does not code any antigen IaIa IaIo Group A IbIb IbIo Group B IaIb Group AB IoIo Group O

Question 27

Multiple Alleles Rabbit Fur

Answer 27

C - dominant Ch Cch Ca Ch - dominant Cch and Ca Cch - dominant Ca Ca - recessive CC CCh CCch Cca - Agouti ChCh, ChCch, ChCa - Himalyan CchCch, CchCa - Chinchilla CaCa- Albino

Question 28

Autosomes

Answer 28

Non-sex chromosomes

Question 29

Sex Linked Inheritance

Answer 29

Occurs with alleles of genes located on sex chromosomes Y-Linked is confined to males - rare X-linked traits relatively common

Question 30

X linked recessive traits

Answer 30

•reciprocal crosses prod diff results - used in testing for sex linkage •more common in males than females - allele only has to appear once •affected males inherit from mother as Y is from father •Affected females inherit from both parents

Question 31

X Linked Dominant Traits

Answer 31

Trait passed from an affected father to all his daughters (daughter always inherits fathers X)

Question 32

Autosomal Recessive

Answer 32

Parents of an affected individual may not be affected Trait might skip a generation

Question 33

X linked recessive

Answer 33

Same a autosomal recessive but: •more common in males •father must be infected for female to be infected •affected female will pass trait to all sons

Question 34

Autosomal Dominant

Answer 34

At least one parent must be affected If both not all children necessarily infected as heterozygous

Question 35

X-linked Dominant

Answer 35

Same as autosomal but: Affected father will pass trait to all his daughters

Question 36

Mendel's Second Law

Answer 36

During gamete formation, the segregation of the alleles of one gene is independent of the segregation of alleles of another gene

Question 37

What did Mendel's Second Law explain

Answer 37

Law of Independent Assortment Explained by the random arrangement of homologous paid on the equator of the spindle at metaphase I of Meiosis and their subsequent separation during anaphase I

Question 38

Human genes and chromosomes

Answer 38

21000 genes 23 chromosome pairs Any single gene may be linked to thousands of other genes

Question 39

Dominance at each of 2 loci cross diagram

Answer 39

Question 40

Different Genetic Situations for Dihybrid Inheritance

Answer 40

Codom, lethality, multiple and sex linkage are possible on each genetic locus

Question 41

Polygenic Inheritance

Answer 41

Many traits governed by cumulative effects of 2 or more genes Colour wheat grain determined by additive effects of A/a and B/b - more A and B = deeper shade of red - 5 shades possible

Question 42

Polygenic Inheritance Diagram

Answer 42

Question 43

What characterisics does polygenic inheritance provide

Answer 43

Quantitative (weight or height) Exhibit normal frequency distribution for a continuous variable- particularly when further influence of env added

Question 44

Epistasis

Answer 44

Interference of Gene Expression by alleles at another locus e.g. W/w G/g W suppress G/g so G/g only expressed when w/w Purple Flower: Precursor -gene A-> Intermediate -gene B-> Purple Pigment