1. Genetics and Inheritance Part 1
Human Biology
Chapter 19
Genetics and Inheritance Part 1
Creature

2. Genetics Terminology
Genes: DNA sequences that contain instructions for building proteins or RNA molecules with enzymatic functions
Chromosomes: structures within the nucleus, composed of DNA and protein
Humans: 23 pairs of chromosomes
22 pairs of homologous chromosomes, also known as autosomes
1 pair of sex chromosomes, which determine gender

3. More Terminology Homologous chromosomes
One member of each pair is inherited from each parent
Look alike (size, shape, banding pattern)
Not identical: may have different alleles of particular genes
Alleles: alternative forms of a gene
Alleles arise from mutation

4. autosome carries the same genes at the locus
Pair of autosomes. Each
autosome carries the same
genes at the locus
Gene locus (plural loci). The location of a
specific pair of genes
A pair of genes. Normally both genes have
the same structure and function
Alleles. Alternative versions of the same
gene pair
Figure 19.1

5.
Both accessed January 29, 2012.

6. Traits can be inherited as
Autosomal dominant
Autosomal recessive
Sex linked
Codominant
Incompletely dominant
Polygenic
Multiple alleles
Epistatic
Linked
Maternal genes
And more!

7. Genotype Is the Genetic Basis of Phenotype
Genotype: an individual’s complete set of alleles
Phenotype: observable physical and functional traits
Examples
Hair color, eye color, skin color, blood type, disease susceptibility
Phenotype is determined by inherited alleles and environmental factors
Punnett square analysis predicts patterns of inheritance

8. Gregor Mendel Developed Basic Rules of Inheritance
Worked with pea plants in the 1850s in Austria
Did multiple genetic experiments to develop basic rules of inheritance
Law of segregation
Gametes carry only one allele of each gene
Law of independent assortment
Genes for different traits are separated from each other independently during meiosis
Applies for genes on different chromosomes

9. Dominant Alleles and Recessive Alleles
Dominant allele (dominates)
Masks or suppresses the expression of its complementary allele
Always expressed, even if heterozygous
Recessive allele (recedes)
Will only be expressed if individual is homozygous for the recessive allele
Dominant alleles are not always more common than recessive; sometimes they may be rare in a population

10. a) Mendel’s first cross yielded all yellow-pea plants
Key:
Y = yellow peas
y = green peas
Yellow pea
Green pea
a) Mendel’s first cross yielded all
yellow-pea plants
b) Mendel’s second cross
between two of the offspring
of his first cross yielded 75%
yellow-pea and 25% green-
pea plants
Figure 19.3

11. Incomplete Dominance
Heterozygous phenotype is intermediate between that of
either homozygote
Examples
Hair
Straight hair: HH
Wavy hair: Hh
Curly hair: hh
Pink color in some flowers
Familial hypercholesterolemia
Dominant/recessive symbols used here. Alternatively use H1 , H2, since not actually dom/rec.

12. Codominance Codominance: products of both alleles are expressed
Examples
Genes for ABO blood types
Sickle-cell gene
Roan coloration in mammals

13. Genes A and B gene are codominant
Genes A and B gene are codominant. Alternatively IA or I B or i symbols for alleles.
An individual heterozygous for the A and B genes will be blood type AB, expressing both A and B antigens on red blood cells
Type A
Type B
Type AB
Type O
Antigen A
Antigen B
Antigens A and B
Neither A nor
B antigens
Red blood cells
Possible
genotypes AA AO BB BO AB OO
Figure 19.10

14. Two different alleles of hemoglobin gene:
Female
Two different alleles of hemoglobin gene:
HbA: encodes normal hemoglobin
HbS encodes sickle cell hemoglobin
Key:
HbA = normal hemoglobin
HbS = sickle-cell allele
Sickle-cell
trait
Normal
Male
Sickle-cell
anemia
Sickle-cell anemia: HbS HbS (homozygous)
Sickle-cell trait: HbA HbS (heterozygous)
Affected individual makes both types of hemoglobin
Figure 19.11