Mendelian Genetics Flashcards
What is step 1 of Mendel’s Pea Plant Experiments?
Grew true breeding plants and called this the P generation (parent)
-Had true bred purple and white flowering plants
What is step 2 of Mendel’s Pea Plant Experiments?
Set up monohybrid crosses:
- True bred plant with purple flower crossed with true bred plants with white flowers
- Produced an F1 Generation which all had purple flowers
-Showed that purple was the dominant factor and white was the recessive factor
What is step 3 of Mendel’s Pea Plant Experiments?
F1 generation self fertilised
- White flowering plants reappeared in F2 generation
- 705 plants with purple flowers and 224 with white flowers
- Approximately 3:1 ratio
What did mendel conclude?
- An organism inherits 2 factors (known as alleles) for a characteristic:
- Heriditary particles (Genes)
- Alternative Forms (Alleles)
-When the plant reproduces these 2 characteristics separate (segregate during gamete formation and end up in different gametes)
What is Mendel’s law of segregation?
- Each gamete gives one factor (allele)
- Each offspring gets one factor from each parent
- Random fusion during fertilisation
What is the rule of dominance?
- homozygous dominant factors express dominant response
- Heterozygous factors express dominant response
- Homozygous recessive factors express recessive response
What are the ratios in mendels plant experiment?
3: 1 ratio of phenotypes
1: 2:1 ratio of genotypes
What are alleles?
Different versions of the same gene
-Occurs due to variance in the sequence of nucleotide bases at the specific locus of the gene
What is mendels law of independent assortment?
Genes get shuffled - these many combinations are one of the advantages of sexual reproduction
What are dihybrid crosses?
cross between two different lines/genes that differ in two observed traits. In this case crossing yellow round peas with green wrinkled peas
What is the ratio created in dihybrid cross?
9:3:3:1
What are some recessively inherited disorders?
Cystic fibrosis, Tay Sachs disease, Sickle Cell Anaemia
-People can be carriers if only containing one recessive allele
What are some dominantly inherited disorders?
Huntington’s disease, Achondroplasia (dwarfism)
How does Huntington’s disease continue through generations?
Disease has no obvious effect until 35-45years old, usually after reproduction has occurred causing allele to be passed on to the next generation
How many chromosomes does a diploid cell have?
2n = 46chromosomes (2sets)
How many chromosomes does a haploid cell have?
n = 23chromosomes (1 set)
What is mitosis?
Process by which cells are replicated for growth, repair
What is meiosis?
Process by which gametes are produced
-produces 4 daughter cells, each haploid containing a single set of chromosomes
What happens in meiosis?
Meiosis I:
-reductional division: homologous pairs are separated reducing the number of chromosomes by half
IPMAT
Meiosis II:
-equational division: -sister chromatids are seperated producing 4 haploid gametes (analogous to mitosis)
How does independent assortment of chromosomes have an effect during meiosis?
- Leads to an individual producing a collection of gametes that differ greatly in the combinations of the chromosomes inherited from parents
- 2^23 is the number of possible combinations of maternal and paternal chromosomes (8.4million)
- Each chromosome is not entirely maternal or paternal origin because of the process of crossing over
What is crossing over?
The DNA of 2 non-sister chromatids are joined and pieces of each chromatid are exchanged beyond the cross over point
- Produces recombinant chromosomes
- Average of 1-3 crossing over events per chromosome pair
- Occurs in Prophase I
What is random fertilisation?
Any two gametes can come together to fertilise.
- in humans there are 70trillion diploid combinations
- adds to genetic variation
What are the complications with Mendel’s laws?
Genotypic ratios follow Mendel’s laws but phenotypes do not
What is incomplete dominance?
One trait is not really dominant over the other
-The phenotype of the heterozygous is intermediate between the phenotype of dominant and recessive traits - blending of the traits
What is codominance?
When both alleles for a trait are expressed in heterozygous offspring
-the two dominant genes are expressed at the same time
Eg. ABO blood groups
How are blood groups determined?
3 alleles for a single gene:
I(a) - Dominant for A group
I(b)- Dominant for B group
i - Recessive for O group
4 Phenoypes: A, B, AB, O
- I(a) and I(b) are co-dominant so both carbohydrates are present when they exist together in a genotype
- I(a) and I(b) are dominant over the i allele
What is Pleiotropy?
Most genes have multiple phenotypic effect (pleiotropy)
What is epistasis?
Phenotypic expression of a gene at one locus affects another gene at a different locus eg, labrador coat colour
-Second gene determines pigment production, if there is no dominant pigment allele then the dog will be yellow irrespective of the other alleles
What is polygenetic inheritance?
- One character is influenced by many genes
- Eg, height, skin colour
What instances occur where Mendel’s laws do not apply?
- Mitochondrial Inheritance -mtDNA is solely inherited through the maternal line
- LInkage - two genes that are close together physically
- Linkage disequilibrium - two alleles that are not inherited seperately
