Chapter 22 - Inheritence Flashcards
What were the two principles relating to inheritance put forward by Austrian Monk Gregor Mendel?
- The various hereditary characteristics were controlled by factors (one called GENES) and that these occurred in pairs.
- During the formation of the Gametes (in humans, the eggs and the sperm), the pair of factors separate.
- each gamete Receives only one set of factors or genes, the other set going to the other gamete.
- Gametes unite at fertilisation, allowing different combinations of genes to come together.
What are genes?
A segment of DNA located in a chromosome containing information for a specific trait.
Genes can also suppress and enhance these traits it’s responsible for.
(Acetylation and methylation)
What is Cytology?
Cytology is a feild in biology - the study of cells.
Mendel - Walter Sutton
Walter Sutton (young American graduate student) linked the work of Mendel to that of the cytologists.
His observations of the behaviour of chromosomes during meiosis and speculation of Mendel’s speculation on the separation of the hereditary factors during the formation of Gametes.
- led Sutton to suggest
HEREDITARY FACTORS, OR GENES, WERE LOCATED IN THE CHROMOSOMES.
- this important hypothesis contained in a research paper he published in 1903, led to the CHROMOSOME THEORY OF HEREDITARY.
List some dominant human traits
- Free earlobes
- Broad lips
- Long eyelashes
- Broad nostrils
- Abundant body hair
- Curly hair
- Mongolian eye fold
- Astigmatism
- Roman nose
- Huntington’s disease
- Achondroplasia
- Normal enzyme production
- Normal pigmentation
- Tongue rolling
What are some recessive traits in humans
- Attacked earlobes
- Thin lips
- Short eyelashes
- Narrow nostrils
- Little body hair
- Straight hair
- No eye fold
- Normal vision
- Straight nose
- No disorder
- Normal build
- Phenylketonuria
- Albinism
- Non rolling tongue
Define Allele
An alternative form of a gene
- an individually normally has one or 2 alleles for each gene
Homozygous Vs Heterozygous
Homozygous: the situation where an individual has the same alleles for a particular characteristic- pure breeding
Heterozygous: the situation where an individual posses different alleles for a particular trait - hybrid
What is a Cross vs. Monohybrid Cross
A cross is the mating of 2 organisms
In A monohybrid Cross only one pair of contrasting characteristics is studied.
- a cross between two organisms with different variations at one genetic chromosome of interest
- this cross is governed by two or multiple variations for a single locus.
Explain Mendel’s discoveries
- Mendel conducted breeding experiments with the edible garden pea ‘Pisum’
* was impressed by the fact that it possess a number of characteristics/traits that were expressed in contrasting forms.
* studied 7 pairs of contrasting in which alternatives were easily identifiable - Using Pure-bred pea plants he crossed/interbred these purebred plants with contrasting traits.
- The progeny produced where hybrids because they genetic information from both parent plants.
- the trait showed by the hybrid plant - dominant
- the trait appearance masked by the hybrid - recessive - Then he allowed the hybrid plants to self-pollinate creating a second generation of plants were produced.
- 3:1 ratio (dominant : recessive) was shown by this generation - From these results he concluded that the hereditary factors/genes were unchanged as they passed from one generation to the next.
- Further reasoned that each pea plant had 2 hereditary factors for each characteristic under his study, and called it the PRINCIPLE OF SEGREGATION
Explain the principle of segregation
During the formation of Gametes, genes (factors) are separated or SEGREGATED - Each gamete receiving only one factor or gene for each trait.
As offspring are formed by the union of male and female gamete - each offspring recurved one gene for each characteristic from each parent.
Define progeny
The offspring
What is pure breeding?
Pure breeding are those individuals that produce the same characteristic for a particular trait.
First filial generation vs second filial generation
First - denoted by F(1)
Second - denoted by F(2)
The F1 (first filial) generation consists of all the offspring from the parents.
The F2 (second filial) generation consists of the offspring from allowing the F1 individuals to interbreed
What are punnet squares?
square diagram that is used to predict the genotypes of a particular cross or breeding experiment.
R.C. Punnet, a British geneticist
What are the 5 complete dominance/recessive related diseases in humans? Autosomal
- Huntington’s Disease (Dominant)
- Phenylketonuria (recessive)
- Thalassaemia (recessive)
- Cystic fibrosis (recessive)
- Tay - Sachs disease (recessive)
Explain Huntington’s Disease
In humans Huntington’s disease is CONTROLLED BY A DOMINANT GENE ALLELE
- mutated on chromosome 4. Mutated protein - huntingtin
Passed down from ONE GENERATION TO the NEXT.
SYMPTOMS: appear in life approximately after 30-40yrs age
Affects - part of brain (nerve cells) that controls movement.
Results in uncontrollable jerky movements, involuntary flailing of arms and legs, rigidity-ness of body, affects speech, ability to think and swallow, dementia - memory loss
No cure - treatment can either slow progression/reduce magnitude of symptoms
Need one ALLELE ONLY - Coz completely dominant
Uncommon 1:20 000
Explain Phenylketonuria
PKU is a rare disease controlled by a RECESSIVE ALLELE.e
Caused by mutated gene on chromosome 12 for the enzyme that breaks down phenylalanine to tyrosine.
This means the body cannot break down this Amino Acid and therefore build up of toxic phenylalanine causing
- mental retardation
Treatment: controlled diet - low levels of this protein phenylalanine found in milk, eggs and meat
Need 2 recessive allles - recessive
- OFTEN SKIPS A GENERATION
Tested after birth via Heel prick test
1:50 000
Examples of Co -Dominance not in humans
- Speckled Chook - Black chicken (B) and White Chicken (W) genotype results (BW) a speckled chicken (not grey!)
- Roan Coloured Cattle - red and white colour genes (RW) makes the cows coat have red and white hairs
Explain Examples of Co-Dominance in Humans
- ABO blood group (I^(A) or (B) or (AB) or (O)
2. Sickled cell anemia
Explain Sickled Cell anemia
In sickled cell anaemia (inherited by people of black African ancestry 40%)
It results in the red blood cells being in a crescent-like or sickled shape.
If homozygous- the disease is fatal as the sickled RBCs do not carry as much oxygen as normal, they can stick together and block small blood vessels.
- sometimes death
Heterozygous individuals are carriers and suffer from Sickle -cell trait.
(Co-dominant) The sickle cell trait gauges certain advantages to those who have it; provides a a degree of immunity to malaria (a disease that is found where sickle celled gene are prevalent)
Define Multiple Alleles
There are more than 2 alleles for a particular characteristic.
The position of that gene on a chromosome is called multi-allelic
What is polymorphism?
Polymorphism is where many different physical forms can result from the various alleles at a single gene location.
Situations where multiple alleles are involved are referred to as polymorphic
What is a Carrier?
People who carry a recessive but do not show the recessive phenotype are known as carriers.
