Genetics

Question 1

Genes

Answer 1

DNA units in chromosomes coding for a particular protein or characteristic

Question 2

Allele

Answer 2

• A form of a particular gene
• Alleles occupy the same locus of a particular chromosome
• One gene/allele is inherited from each parent

Question 3

Artificially crossed

Answer 3

Breeding controlled by humans, usually to create organisms with specific traits.

Question 4

Dominant allele

Answer 4

An allele which is expressed over a recessive allele

Question 5

Recessive allele

Answer 5

An allele not expressed in the presence of a dominant allele

Question 6

Genotype

Answer 6

The genetic makeup of a particular organism

Question 7

Phenotype

Answer 7

• The observable traits,
• determined by both genotype and the organisms environment

Question 8

Locus

Answer 8

Specific place or position (on a chromosome)

Question 9

Offspring

Answer 9

Children or young of particular parent(s)

Question 10

Selective breeding

Answer 10

Intentional mating of two organisms to promote specific trait(s)

Question 11

Self pollinate

Answer 11

Transfer of pollen from anther to stigma of same flower or plant

Question 12

Pure/true-breeding

Answer 12

Self fertilized or two pure-breeding organisms consistently produce offspring with the same particular trait

Question 13

Trait

Answer 13

• In genetics, a characteristic of an organism.
• Some are visible e.g. Eye colour
• Some not easily seen e.g. Blood type

Question 14

Who was Gregor Mendel

Answer 14

• Austrian monk in mid 1800’s
• Quantitatively showed that parent plants pass on factors of inheritance (genes)
• some factors not expressed but still able to be passed on

Question 15

Mendel’s focus group and what he did with them

Answer 15

• Pea plants
  
  • Thousands of selective breeding events e.g. forcing self and cross-pollination examining particular traits
  • Starting with true-breeding plants for a particular trait he crossed them with other true-breeding plants
  • Recorded traits of offspring

Question 16

Why pea plants for Mendel’s experiments?

Answer 16

• grow and reproduce quickly
• many traits in one species
• easy to control reproduction (naturally self-fertilizing but can be cross-fertilsed)
• True-breeding strains for particular traits already available to him

Question 17

Seven traits Mendel studied in peas

Answer 17

• Seed shape
• seed colour
• flower colour
• pod shape
• pod colour
• flower position
• plant length

Question 18

Mendel’s three laws

Answer 18

• Segregation
• Dominance
• Independent assortment

Question 19

Law of segregation

Answer 19

• If there are two alleles controlling a trait, these alleles separate and go to different gametes when parent reproduces.
• During meiosis alleles randomly divided between different gametes
• Thus 2x2 possible combinations of the same alleles in successive generations are possible

Question 20

Law of dominance

Answer 20

If an organism has different alleles, the trait of one of these will be visible (domnant) whole the other will be hidden (recessive)

Question 21

Symbols for dominant/recessive alleles

Answer 21

• Capital letter for dominant and lower case letter for recessive.
• Letters with a different form of capital vs lower case are typically used
• e.g. Dd or Tt (instead of e.g. Pp or Oo)

Question 22

Homozygous individual

Answer 22

An individual with only one kind of allele for a particular gene

Question 23

Heterozygous individual

Answer 23

An individual with two kinds of allele for a particular gene

Question 26

Law of independent assortment

Answer 26

Different traits are passed on independently of one another so that combinations of traits in parents do not always match combinations of traits in offspring.

Question 27

Two cats both have brown fur. They have the following alleles: Bb and BB. Which is the same - their genotype or phenotype?

Answer 27

Phenotype

Question 28

Two cats both have brown fur. They have the following alleles: Bb and BB. Which one is homozygous?

Answer 28

* BB as it has the same alleles. * Bb is heterozygous.

Question 29

Monohybrid cross

Answer 29

* Genetic cross between two individuals * Each of whom has different alleles for a single trait * And only two different possible alleles * can be heterozygous or homozygous individuals

Question 30

F1 generation

Answer 30

* First filial * Filial means the relation of a child to parent

Question 31

Incomplete dominance

Answer 31

* When alleles show incomplete or partial dominance * Neither characteristic is dominant over the other * Offspring can show a new, mixed characteristic when heterozygous * E.g. White flower crossed with a red flower -\> pink flower

Question 32

Co-dominance

Answer 32

* Co-existing characteristics because of equally dominant alleles * Both are present in the phenotype when heterozygous * E.g. Black cow crosses with a white cow -\> spotted black and white cow

Question 33

Blood groups - type of dominance

Answer 33

Co-dominance

Question 34

Possible blood types in humans

Answer 34

* A * B * AB * O

Question 35

Rhesus blood factor

Answer 35

* Rhesus blood antigen * Two alleles Rh+ and Rh- * Rh+ is dominant and expresses a cell surface antigen * Rh- is recessive and does not express an antigen

Question 36

Polygenic inheritance

Answer 36

* Traits that are determined by more than one gene * Results in continuous variation in a population * E.g. Hair colour, eye colour, intelligence

Question 37

Dihybrid crosses

Answer 37

* Examining inheritance of two different traits at the same time * E.g. Flower colour AND seed shape

Question 38

Pattern of inheritance with two true breeding dihybrid individuals

Answer 38

9:3:3:1

Question 39

Pedigree diagram

Answer 39

* Diagrams showing family relationships * Older generations are at the top * Symbols of a square = males and circles = females * Horizontal lines directly connecting individuals show breeding * Vertical lines with horizontal connectors show offspring * A key (shading) indicates the known phenotypes

Question 40

Pedigree diagram uses

Answer 40

* To determine the type of inheritance * Evaluate the inheritance of genetic conditions in a particular family * By genetic councilors to advise families with genetic diseases

Question 41

Sex chromosomes

Answer 41

* The sex of an individual is determined by the presence of X and Y chromosomes. * Also called gonosomes. * XX = female XY = male

Question 42

Chance of male vs female offspring

Answer 42

* Determined by the sperm * 50% that it contains a Y-chromosome = XY male individual * 50% that it contains an X-chromosome = XX female individual

Question 43

Autosomes

Answer 43

Chromosome pairs 1-22 not involved in determining the sex of an individual

Question 44

Sex-linked genes

Answer 44

* Genes carried on the sex chromosomes * X-chromosome has over 1000 genes * Y-chromosome only 78 genes

Question 45

Male risk of sex-linked disorders

Answer 45

* Since male have only one X-chromosome they have a higher risk of a genetic disorder found on the X-chromosome. * Even if that disorder is recessive for females, since males have only one X-chromosome, they are still affected.

Question 46

Examples of sex-linked disorders

Answer 46

* Muscular dystrophy * Haemophilia * Cleft palate syndrome * Colour blindness

Question 47

Haemophilia

Answer 47

* X-chromosome linked * Recessive for females Lack of a gene for blood clotting * Affected individual (male with this faulty gene) bleeds excessively * Females homozygous for this faulty gene usually aborted before birth.

Question 48

Muscular dystrophy

Answer 48

* A degenerative disease most common in boys. * X-chromosome linked recessive inheritance pattern. * Progressive loss of muscle function.

Question 49

Genetic counselling

Answer 49

Advised if: * Have a child or family history of a genetic condition, chromosome abnormality of birth defect * You or family have a history of miscarriages or stillbirths They help you understand risks of passing inherited conditions on to your children