Unit:4 Mendel's Laws of Inheritance and Genetic Principles

Genetics

Study of heredity and genetic variation.

Johann Gregor Mendel

Father of modern genetics; conducted pea plant experiments.

Blending inheritance

Unsupported theory; traits blend from parents.

Genes

DNA sequences that encode traits and proteins.

RNA

Molecule that translates genes into proteins.

Proteins

Final products of gene expression determining traits.

Phenotype

Observable traits of an organism.

Genotype

Individual's specific DNA sequence for a gene.

Alleles

Gene variants at the same locus on chromosomes.

Homozygous

Organism with two identical alleles for a gene.

Heterozygous

Organism with two different alleles for a gene.

Law of Dominance

Dominant allele masks recessive allele in phenotype.

Law of Segregation

Genes segregate equally into gametes during meiosis.

Diploid organism

Organism with two sets of chromosomes.

Gametes

Haploid cells that unite during fertilization.

True-breeding

Organisms that consistently produce offspring with same traits.

F1 generation

First filial generation from parental cross.

F2 generation

Second filial generation from F1 self-cross.

Dominant allele

Allele that expresses its trait in heterozygotes.

Recessive allele

Allele that expresses its trait only in homozygotes.

Punnett square

Tool to predict offspring genotypes from parental genotypes.

Mendel's experiments

Used pea plants to study inheritance patterns.

Seed color

Trait governed by a single gene with two alleles.

Yellow-seed allele

Dominant allele for yellow seed color.

Green-seed allele

Recessive allele for green seed color.

3:1 ratio

Phenotypic ratio observed in F2 generation of monohybrid cross.

Physical basis of segregation

First meiotic division segregates homologous chromosomes.

Characteristic

A feature influenced by genes, like hair color.

Trait

Specific expression of a characteristic, like black hair.

Independent Assortment

Alleles of different genes sort independently into gametes.

Dihybrid Cross

Cross between two true-breeding parents for two traits.

Phenotypic Ratio

Observed ratio of different phenotypes in offspring.

Punnett Square

Grid used to predict genetic cross outcomes.

Monohybrid Cross

Cross studying one characteristic between true-breeding parents.

F1 Generation

First filial generation from a genetic cross.

F2 Generation

Second filial generation from crossing F1 offspring.

Test Cross

Cross to determine genotype of dominant phenotype.

Unit Factors

Pairs of alleles controlling traits in inheritance.

Probability

Likelihood of an event occurring, between 0 and 1.

Complete Dominance

Dominant allele completely masks recessive allele.

3:1 Ratio

Phenotypic ratio in monohybrid crosses with dominance.

9:3:3:1 Ratio

Phenotypic ratio in dihybrid crosses with dominance.

Branch Diagram

Visual method for calculating genetic probabilities.

FOIL Method

Technique for determining gamete combinations from genotypes.

Zygote

Fertilized egg formed from gamete fusion.

Meiosis I

First division in meiosis, separating homologous chromosomes.

Tetrads

Paired homologous chromosomes during meiosis.

Random Orientation

Random arrangement of tetrads during meiosis I.

Dominant Trait

Trait expressed in heterozygous condition.

Recessive Trait

Trait expressed only in homozygous condition.

Unknown Genotype

Genotype of an organism not determined yet.

Equal Probability

Each outcome has the same likelihood of occurring.

Independent Outcomes

Events whose outcomes do not affect each other.

Probability of A or B

Calculated as P(A) × P(B) for independent events.

Double 6 Probability

P(Die 1 = 6) × P(Die 2 = 6).

Genotype Inference

Determining genotypes from known phenotypic ratios.

Pedigree

Family tree showing inheritance patterns.

Autosomal Genes

Genes located on non-sex chromosomes.

Sex-linked Genes

Genes located on X or Y chromosomes.

Simple Mendelian Genes

Traits governed by a single dominant-recessive pair.

Incomplete Dominance

Heterozygote phenotype is intermediate between parents.

Codominance

Both alleles expressed equally in heterozygotes.

Multiple Alleles

More than two alleles exist for a gene.

Pleiotropy

Single gene affects multiple phenotypes.

Polygenic Traits

Traits influenced by multiple genes.

Transcription

Process of converting DNA to mRNA.

Central Dogma

Flow of genetic information: DNA → RNA → Protein.

Codon

Three mRNA nucleotides coding for one amino acid.

Genotypic Ratio

Ratio of different genotypes in offspring.

Phenotypic Ratio Example

1:2:1 for red:pink:white in snapdragons.

Fluffy Trait

Fluffy is dominant over smooth in dogs.

Spotted Trait

Spotted is dominant to solid color in dogs.

Heterozygote

Individual with two different alleles for a gene.

Carrier

Individual with one recessive allele, not expressing it.

Affected Individual

Individual expressing a genetic trait or disease.

tRNA

Transfer RNA that carries amino acids to ribosome.

rRNA

Ribosomal RNA, a component of ribosomes.

RNA-i

Interference RNA that regulates gene expression.

Gene

DNA segment transcribed with functional output.

Promoter

DNA region initiating transcription by RNA polymerase.

Regulatory Regions

DNA segments that modulate RNA polymerase activity.

Template Strand

DNA strand used for mRNA synthesis.

Nontemplate Strand

DNA strand complementary to the template strand.

RNA Polymerase

Enzyme synthesizing RNA from a DNA template.

Co-transcriptional Translation

Simultaneous transcription and translation in prokaryotes.

Eukaryotic mRNA Processing

Modifications for stability and transport of mRNA.

5' Cap

Modified nucleotide protecting mRNA and aiding translation.

Poly-A Tail

String of adenines added to mRNA's 3' end.

Exons

Expressed protein-coding sequences in mRNA.

Introns

Non-coding sequences removed during mRNA processing.

Splicing

Process of removing introns and joining exons.

Ribosome

Complex of RNA and proteins synthesizing proteins.

A Site

Ribosome site where new tRNA arrives.

P Site

Ribosome site holding growing polypeptide chain.

E Site

Ribosome site where empty tRNA exits.

Aminoacyl tRNA

tRNA bound to its corresponding amino acid.

Aminoacyl tRNA Synthetase

Enzyme recharging tRNA with specific amino acids.

Initiation Factors

Proteins aiding ribosome binding to mRNA.

Translocation

Ribosome movement along mRNA during translation.

Release Factor

Protein terminating translation at stop codons.