Chapter 5 Heredity

Section 5.1 Mendel & Peas

Heredity  Passing of genetic traits from parent to offspring How Traits are Inherited  Genes made up of DNA  Genes found on chromosomes  Genes control all traits  Pairs of genes separate when chromosomes separate

 Known as Father of Genetics  Discovered the principles of heredity by studying pea plants  Noticed that traits can skip a generations

 Chose peas because they grow quickly, many different kinds, & are self-pollinating (has both male & female reproductive parts – pollen from one flower can fertilize same flower)  Mendel able to grow true breeding plants (all offspring have same trait as parents)  Peas can also cross-pollinate (pollen from one plant fertilizes the egg of another plant)  Pollen carried by insects, wind, & other animals

 Mendel studied one characteristic at a time (seed shape, plant height, flower color)  Another example: hair color in humans is a characteristic & different forms, like red, brown, or blonde, are traits

Dominant vs. Recessive  Dominant traits are always expressed (observed) in first generations when parents w/different traits are bred  Recessive traits are masked or hidden in first generations but reappear in the second generation when parents w/different traits are bred

 Mendel decided to figure out ratio of dominant to recessive traits  Ratio is relationship between two different numbers (often shown as a fraction) Example: 3:1

Section Traits & Inheritance

Genes:  Set of instructions for an inherited trait Alleles:  Different forms of a gene (ex. all have a gene for eye color but each have different alleles such as blue, brown, green)

Dominant  trait that is always expressed  shown with a capital letter (B)  can be homozygous or heterozygous

Recessive  trait that is not expressed when dominant allele is present; dominant allele mask or covers it up.  shown with a lowercase letter (b)  must be homozygous for recessive trait to be expressed

Purebred:  Both alleles are the same (ex. BB or bb)  Can be homozygous dominant (BB) or homozygous recessive (bb)  Means the same as Homozygous Hybrid:  Both alleles are different (ex. Bb)  Means the same as Heterozygous

Phenotype:  Physical appearance or what you see  Example: such as brown eyes vs. blue eyes. Genotype:  Genetic makeup of an organism  Set of alleles can be - Bb, BB, or bb

Punnett Square  diagram that shows the expected offspring of 2 parents (shows all the possibilities)  Capital letter = dominant allele  Small letter = recessive allele  Letters of one parent written along top of square and letters of other parent written along the left side of the square  Cannot always figure out genotype by looking at the phenotype

Example: First Generation  Alleles from homozygous tall parent  Alleles from homozygous short parent  Genotypes of offspring:  Phenotype of offspring:

Second Generation  Alleles from heterozygous tall parents  Genotypes of offspring:  Phenotype of offspring:

Probability  Predicts the chance that something will happen (ex. coin toss 1 out of 2 or a 50% chance)  Think lottery, weather forecasting.

Incomplete Dominance  Phenotype is intermediate (in between) to the 2 homozygous parents  Neither allele for color was dominant – colors blended to make new color  Example: four o’clock flowers have alleles for red and white flowers Red x White = Pink

One gene-Many Traits  Sometimes one gene can influence more than 1 trait  Single trait that is produced by a combination of many genes  Example: In tigers the gene for fur color also carries the gene for eye color white tiger - -> white fur caused by single gene but this gene also influences other traits like eye color (tiger has blue eyes)

Section 5.3 Meiosis

Asexual Reproduction  Only one parent cell is needed (these cells have 46 chromosomes)  Structures are copied and then parent cell divides making two identical cells (this is Mitosis & occurs in body cells)  Daughter cells are identical (46 chromosomes)  Bacteria, single celled organisms

Sexual Reproduction  Two parent cells join together to form an offspring that are different from both parents  Two sex cells join – one from each parent (each sex cell has 23 chromosomes)

Sexual Reproduction  Human sex cells join (1 egg, 1 sperm)  Human sex cells have 23 chromosomes  Process is known as Meiosis

Meiosis  Process in cell division in which number of chromosomes are reduced to half the original number  Cells go through cell division 2 times

Meiosis  Sex cell in the female is the egg (23 chromosomes)  Sex cell in the male is the sperm (23 chromosomes)  Sperm and egg join to make offspring with 46 chromosomes ( = 46)

Homologous Chromosomes Chromosomes that carry the same set of genes (like a pair of shoes)

Steps of Meiosis 1.Starts with parent cell (46 chromosomes) 2.Interphase-chromosomes copy (sister chromatids) 3.Prophase I -chromosomes become visible; nuclear membrane disappears 4.Metaphase I -homologous chromosomes pair up, pairs of chromosomes line up at the center of the cell

Steps of Meiosis 5. Anaphase I - homologous pairs start to separate 6. Telophase I -homologous pairs move to opposite ends of cell; nuclear membrane reforms 7. Now you have 2 cells

Steps of Meiosis 8.Prophase II - chromosomes become visible; nuclear membrane disappears 9.Metaphase II - chromosomes line up at equator of cell 10.Anaphase II - sister chromatids of chromosomes separate

Steps of Meiosis 11.Telophase II - chromatids move to opposite ends of the cell; nuclear envelope reforms 12.Cytokinesis - cytoplasm divides 13.END with 4 sex cells- each has ½ number of chromosomes (23)

Sex Chromosomes  X and Y chromosomes  Male has XY  Female has XX  All eggs have an X chromosome  Sperm will EITHER have an X OR a Y chromosome  When they join determines if offspring is male or female

Sex Linked Disorders  Some inherited conditions are carried on a sex chromosome  Females get 2 X chromosomes-if one is unhealthy they have a back up  Males only get one X chromosome-if it is unhealthy they will have a disorder

Color-Blindness  Sex linked disorder  Trouble distinguishing red from green  Males are color-blind more often than females  If mom has an allele for colorblindness and passes it on to a son he will be color blind  Females must have a dad who is color-blind and a mom who carries the color-blind allele to be color-blind

Hemophilia  Sex linked disorder  Blood does not clot properly  People with this disorder bleed a lot from small cuts  Can be fatal

Sickle-cell anemia (recessive disorder)  Homozygous recessive disorder  Blood cells are sickle shaped (like a C) instead of normal disc shaped (like a C) instead of normal disc shaped  Cannot deliver enough oxygen  Blood cells get stuck together  Most people with disorder die as children

Cystic fibrosis (recessive disorder)  Homozygous recessive  Normally thin fluid lubricates lungs but people with CF have Thick mucus clogs lungs  Makes it hard to breathe causes lung damage  1 in 20 people carries a recessive allele for this disorder

Pedigree Charts  Family tree that traces a trait in a family  Purebred dogs might have a pedigree chart  Used in tracking disease & genetic counseling

Pedigree Charts Square = male Shaded in = has trait Circle = female Half shaded = carrier Not shaded = normal Not shaded = normal

Selective Breeding  Organisms with desirable characteristics are mated  Humans have been selectively breeding for thousands of years (10,000)  Started after the last ice age  Examples: chickens that produce larger eggs, dog breeding, thorn-less roses