D3.2: Inheritance

Question 1

What is inheritance?

Answer 1

Inheritance refers to a trait passed from parent to offspring during reproductions

DNA -> molecules of inheritance for all living organisms

Question 2

What are haploids and diploids?

Answer 2

Haploids:
One chromosome of each type
Ex: gamete

Diploids:
Two chromosomes of each type
Ex: zygote

Question 3

What are gametes?

Answer 3

Sex cells of an organism
One copy of each chromosome -> haploids

In humans: sperm and egg (ovum) cells with 23 single chromosomes
- egg is larger -> contains food for growing embryo
- sperm many mitochondria -> release energy for motion

Fuse during fertilization -> zygote -> 46 chromosomes

Question 4

What is sexual production?

Answer 4

Process involving the fusion of nuclei of two gametes (sex cells) to form a zygote (fertilized egg cell) and the production of offspring that are GENETICALLY DIFFERENT FROM EACH OTHER

Results in diploid zygote:
-> two copy of each chromosome
-> two alleles of each gene

Question 5

What does it mean when a genotype is homozygous or heterozygous?

Answer 5

Homozygous:
Both alleles for a particular gene are the same

Heterozygous:
The two alleles for a particular gene are different

Question 6

How did people think inheritance worked before Mendel?

Answer 6

Idea of blending inheritance

Eg: white and purple flower -> light purple intermediate ‘child’

Question 7

What is cross pollination? How do you preform it artificially?

Answer 7

Cross pollination:
One plant fertilizes another plant of the same species

Transfer pollen (male gamete) from one plant to the reproductive parts (ovary) of another

Used by Mendel and his pea plants to investigate height/color of flower/smoothness -> eliminates uncertainty from his data

Question 8

What were the results of Mendel’s crosses?

Answer 8

Establish pea plant population with two different features
Breed until they always produced offspring identical to the parent

Crosses plants with each other -> observe inherited traits

F1: all plants were identical in shape to one of the parents
-> directly contradict blending inheritance
-> conclusions: dominant and recessive

F2: wondered what happened to recessive characteristic -> assumed ‘inherited unit’ produced each phenotype -> did recessive disappear or masked? -> self fertilize F1 generation that displayed dominant trait
-> recessive traits appear

Conclusion:
Phenotypes were determined by a combination of ‘discrete heritable units’ (alleles)
Called particulate inheritance hypothesis

Question 9

What is a monohybrid trait?

Answer 9

One that is controlled by one gene

Question 10

What things are needed when doing a punnets grid?

Answer 10

Gene
Alleles
Parent genotypes
Unique gametes from each parent

Draw Punnett square

List genotype
List phenotype
Ratio of phenotype

Question 11

What is a gene?

Answer 11

A short length of DNA found on a chromosome that codes for a particular characteristic (code for the production of a specific protein)

Question 12

What are alleles?

Answer 12

A different versions of the same gene

Code for the same type of protein
Have difference in a sample base/large sections

New alleles generated by mutation (SNPs)

Question 13

What is the genotype of a person?

Answer 13

The combination of alleles that an individual organism inherits

Can be homo or heterozygous

Question 14

What is the phenotype of a person?

Answer 14

The observable traits or characteristics of an individual
Included by both genes and environment

Examples:
Genes only: blood group, PKU disease, haemophilia
Environment only: scars, body art, language spoken
Both: height, type II diabetes, tanning, coronary heart disease

Question 15

What is a dominant allele?

Answer 15

Alleles that will produce a certain phenotype and will always be expressed if present

Cause:
Dominant allele typically encodes for a functioning protein -> one copy of allele all that is needed in order to make enough of the protein coded for by that gene

Question 16

What is a recessive allele?

Answer 16

Alleles that will produce a certain phenotype that will only be expressed if the genotype is homozygous

Causes:
Recessive allele codes for a nonfunctioning protein
Recessive allele is the normal one and dominant is the mutated version -> need two good for normal function

Question 17

What is phenotype plasticity?

Answer 17

The idea that although genotype remains fixed through an organisms lifetime the way the phenotype is expressed can vary over time

Organisms internal/external environment can influence gene expression
- level of regulatory proteins or transcription factors affected by light, chemicals, drugs, hormones, temperature

Question 18

What is a genetic disease?

Answer 18

An illness caused in whole or in part by a change in the DNA sequence away from the normal sequence
-> Most are caused by recessive gene

Can be:
Dominant: if person has one dominant -> develop disease (Huntington’s disease)

Recessive: person no dominant -> develop disease (cystic fibrosis)

Co-dominant: heterozygotes have different phenotypes than individuals with two copies of either allele (sickle cell disease)

Autosomal: gene located on autosome -> males and females equally affected

Sex-linked: gene located on a sex chromosome -> different pattern of inheritance in males and females (haemophilia)

Question 19

Example of genetic disease (autosomal recessive): PKU

Answer 19

Phenylketonuria
Mutation in PAH gene on chromosome 12

Normal allele (dominant):
Code for functioning phenylalanine hydroxylase
- converts AA phenylalanine -> AA tyrosine

Disease allele (recessive):
Mutation cause production of non-functioning phenylalanine hydroxylase
Phenylalanine not processed effectively -> accumulates + tyrosine deficient -> high concentration phenylalanine neurotoxic -> brain damage (mental disorders, seizures, etc.)

In many counties babies are tested for several genetic conditions upon birth -> PKU included (PKU first conditions for widespread newborn testing)

Diet must have little/no phenylalanine -> limit amount of protein and supplements taken
If children are placed on diet upon birth -> grow normally, no symptom or health problems

Question 20

What are SNPs?

Answer 20

Single Nucleotide Polymorphisms

Variation at a single position in a DNA sequence
Allow multiple alleles

Question 21

What is a gene pool?

Answer 21

Collection of all the genes and various alleles of those genes within a population

Ex: S gene -> in many tree fruit
50 known alleles in apples -> each apple species had different combination
During pollination of pollen with one allele lands on stigma of flower with same allele -> pollen rejected

Question 22

What are the three alleles for blood group?

Answer 22

I -> represents the gene
A -> superscript dominant
B -> superscript dominant

i -> recessive

Question 23

How do the different ABO blood group alleles affect blood type?

Answer 23

Gene codes for enzyme -> alter glycoprotein on plasma membrane of RBC

I^A: add antigen A (acetylgalactosamine) to glycoprotein
I^B: add antigen B (galactose) to glycoprotein
i: add nothing

Question 24

What is incomplete dominance?

Answer 24

One allele not completely dominant over other -> both alleles partially expressed
=> when heterozygous phenotype

Ex:
Marvel of Peru flower color has 2 alleles: C^r and C^w
Heterozygous -> pink -> pigment by red allele diluted

Human hair

Question 25

What is the notation for incomplete dominance/codominance?

Answer 25

Different from simple dominance/recessiveness Capital letter for gene (C for color) Superscript for alleles (C^w for white, C^r for red)

Question 26

What is codominance?

Answer 26

Special incomplete dominance Individual heterozygous -> both alleles expressed equally/both phenotypes present Ex: roan cows Roan coat color from having red hair (Cr) and white hair (Cw) -> both alleles expressed equally