Heredity

Question 1

Gene:

Answer 1

Genetic material on a chromosome that contains the instructions for creating a particular trait

Question 2

Allele:

Answer 2

One of several variations of a gene

Question 3

Locus:

Answer 3

• Location on a chromosome where a gene is located

Every gene has a unique locus on a particular chromosome

Question 4

Homologous Chromosomes:

Answer 4

Pair of chromosomes that contains the same genetic information (gene for gene)

Question 5

Law of Segregation:

Answer 5

• One chromosome from a pair of homologous chromosomes migrates to an opposite pole
Each gamete contains only one copy of each chromosome (and allele)

Question 6

Law of Independent Assortment:

Answer 6

When homologous chromosomes separate, they do not influence which pole any other chromosome pairs go to

Question 7

Incomplete Dominance:

Answer 7

• Both alleles expressed as an intermediate

i.e. Red + white= pink

Question 8

Codominance:

Answer 8

• Both alleles are completely expressed

i.e. Blood type

Question 9

Agglutination

Answer 9

Clumping of blood that results when antibodies attack antigens on foreign blood types

Question 10

Epistasis:

Answer 10

• One gene affects the phenotypic expression of another gene
• Often seen in pigmentation
○ One gene turns the production of a pigment on or off
○ Second gene controls colour or amount of pigment produced
If first gene codes for no pigment, expression of second gene has no effect

Question 11

Pleiotropy:

Answer 11

• Single gene has more than one phenotypic expression

Seems to be responsible for several different characteristics

i..e Gene that codes for whether a seed is round or wrinkled also affects starch metabolism

Opposite of Polygenic inheritance

Question 12

Pleiotropy and Sickle Cell Disease

Answer 12

Allele incorrectly codes of Hb
□Causes RBC to become sickle shaped
Results in damage to heart, lugs kidneys…etc

Question 13

Polygenic Inheritance:

Answer 13

Many traits are not just expressed in 2 or 3 varieties

i.e. Height is expressed as a continuous variation from very short to very tall

Continuous variation usually results from polygenic inheritance
○ Interaction of many genes to shape a single phenotype

Opposite of pleiotropy

Question 14

Linked Genes

Answer 14

• Linked genes reside on the same chromosome
• Cannot segregate independently because they are physically connected
Genes that are linked are usually inherited together

Question 15

Recombination Frequency:

Answer 15

Greater recombination frequency= greater distance between genes

The greater the distance between 2 genes on a chromosome, the more places between the genes that the chromosome can break
(More likely that the 2 genes will cross over during synapsis)

Question 16

Linkage Map

Answer 16

○ Chromosome map created based on recombination frequencies of different genes
Determines sequence of genes on a chromosome

Question 17

Cytological map

Answer 17

Map portraying the true relative positions of genes

Question 18

Sex-Linked Inheritance:

Answer 18

Sex linked/X-linked genes are genes that reside on the X chromosome

Y linked genes are also possible, but rare because there are very few genes on the Y chromosome

Sex linked genetic defects are more common in males than females

Question 19

X-Inactivation:

Answer 19

• In females, one X chromosomes in each cell does not uncoil into chromatin
Instead, forms a Barr body

• Only the allele of the gene on the active X chromosome are expressed 
• One random X chromosome becomes inactive, subsequent daughter cells will have the same X inactivated  (not all cells in females are identical)

Question 20

Barr Body

Answer 20

Chromosome remains as a dark, compact body

Mostly inactive X chromosomes

Genes not expressed

Question 21

X Inactivation- Calico Cats

Answer 21

X chromosome with yellow allele inactivated
- Black allele on active chromosome is expressed

X chromosome with black allele inactivated
- Yellow allele on active chromosome expressed

Different cells with different X inactivated results in patches

Question 22

Non-Disjunction

Answer 22

Failure of one or more chromosome pairs/chromatids to properly segregate

Question 23

Non-Disjunction During Meiosis

Answer 23

Failure of homologous chromosomes (anaphase I) or chromatids (anaphase II) to segregate

Produced gametes with extra or missing chromosomes

Question 24

Non-Disjunction During Mitosis

Answer 24

○ Failure of 2 chromatids (during anaphase) to segregate
○ Produces daughter cells with extra or missing chromosomes
Results in mosaicism

Question 25

Polyploidy

Answer 25

○ All chromosomes undergo meiotic non-disjunction
○ Produces gametes with twice the number of chromosomes
○ If polyploid gamete is fertilized with a similar gamete, then a polyploidy zygote and individual and form
Common in plants

Question 26

Point Mutation

Answer 26

Single nucleotide incorrect

• Most point mutations have deleterious effects on gene function i.e. Sickle cell anemia

Question 27

Substitution

Answer 27

Nt substituted

Question 28

Deletion

Answer 28

Nt missing

Question 29

Insertion

Answer 29

Extra Nt inserted

Question 30

Aneuploids

Answer 30

• Genome with extra or missing chromosomes
• Usually caused by non-disjunction
Most aneuploidy gametes are sterile

Those that survive has genetic defects

Question 31

Down Syndrome

Answer 31

Aneuploidy in chromosome 21

Resulting in trisomy 21

Question 32

Turner Syndrome

Answer 32

Aneuploid

			□ Non-disjunction of sex chromosomes
			□ Sperm either have both sex chromosomes (XY) or no sex chromosomes (O) Individuals with Turner syndrome are physically abnormal, and sterile

Question 33

Chromosome Aberrations

Answer 33

Chromosome segments are changed

Question 34

Duplications

Answer 34

Chromosome segment is repeated on the same chromosome

Question 35

Inversion

Answer 35

Chromosome segment rearranged in reverse orientation on the same chromosome

Question 36

Translocation

Answer 36

○ Segment of a chromosome is moved to another chromosome
○ Down syndrome can also occur after translocation of a chromosome segment from chromosome 21 to chromosome 14
§ Ends up with 2 chromosome 21 and a chromosome 14 with a segment of 21
Same phenotypic effect as trisomy 21