Human Inheritance Essential Questions What are some patterns of inheritance in humans? What are the functions of the sex chromosomes? What is the relationship between genes and the environment?

Patterns of Human Inheritance Human traits are controlled by: single genes with two alleles single genes with multiple alleles many genes that act together

Single Gene with Two Alleles Have 1 dominant and 1 recessive allele Have 2 distinctly different phenotypes Ex. Widow’s Peak, Smile Dimples, Dimpled Chin.

Codominance Having both alleles expressed equally in the phenotype of the organism. Equal degree of dominance of two genes, both being expressed in the phenotype of the individual. Two alleles of a gene pair in a heterozygote that are both fully expressed. Examples of codominance include a person with type AB blood, which means that both the A allele and the B allele are equally expressed. Another example is roan fur in cattle, in which white and red hair is equally expressed.

Examples of Codominance

Single Genes with Multiple Alleles Some traits have more than 2 alleles although a person can have only 2 of those alleles because chromosomes exist in pairs. Each chromosome in a pair carries only 1 allele for each gene. Ex. Human blood type – 3 alleles A, B, O A and B are codominant O is recessive

Traits Controlled by Many Genes Produce a large variety of phenotypes Genes act together as a group to produce a single trait Ex. Height – at least 4 genes Skin color – at least 3 genes

Functions of Sex Chromosomes Sex chromosomes carry genes that determine whether a person is male or female. They also carry genes that determine other traits. GIRL BOY

Girl or Boy Sex Determination People – 46 chromosomes or 23 pairs 22 pairs are homologous (look alike) – called autosomes – determine body traits 1 pair is the sex chromosomes – determines sex (male or female) Females – sex chromosomes are homologous – label XX Males – sex chromosomes are different – label XY

Sex Chromosomes and Fertilization Egg cells all carry an X chromosome. Sperm cells carry either an X or a Y. When a sperm cell with an X chromosome fertilizes an egg cell (X chromosome) the result is a fertilized egg with 2 X chromosomes = girl When a sperm cell with a Y chromosome fertilizes an egg cell (X chromosomes), the result is a fertilized egg with an X and a Y chromosomes= boy

Sex-linked Genes Genes for some human traits are carried on the sex chromosomes. Traits controlled by sex-linked genes are called sex-linked traits. EX. Red-green colorblindness X and Y chromosomes have different genes. Most of the genes on the X chromosome are not on the Y chromosome. An allele on the X chromosome may not have a match on the Y chromosome. Genes for sex-linked traits are located only on the X chromosome (NOT on the Y chromosome)

Sex-Linked Genes Sex-linked genes can have dominant and recessive alleles. In females a dominant allele on one X chromosome will mask a recessive allele on the other X chromosome. In males, there is no matching allele on the Y to mask a recessive allele on the X. If the male gets the sex-linked gene in the X chromosome (even if it is a recessive trait) it will exhibit the affected trait.

Colorblindness Color blindness is the inability to distinguish the differences between certain colors. The most common type is red-green color blindness, where red and green are seen as the same color.

Inheritance of Colorblindness Colorblindness is a trait controlled by a recessive allele on the X chromosome. Many more males have colorblindness than females. Females can be carriers. They have one dominant trait for normal color vision and one recessive trait for colorblindness. They have normal color vision. If the mother passes on the recessive allele on the X chromosome to a son, he will be colorblind. If she passes it onto a daughter, she will also have an X chromosome from her father. If her father has normal color vision, then she will inherit the dominant allele for normal color vision from him and she will have normal color vision.

Color Blindness

The Effect of Environment Many of a person’s characteristics are determined by an interaction between genes and the environment. Several genes work together to determine height. Environment affects height – a poor diet can prevent a person from reaching their potential. Environmental factors can also affect human skills – Ex. Playing a musical instrument – need instruction to play well.

Hares are a bit larger than rabbits, and they typically have taller hind legs and longer ears. Snowshoe hares have a snow-white winter coat that turns brown when the snow melts each spring. It takes about ten weeks for the coat to completely change color. Himalayan Rabbits & temperature

Human Genetic Disorders Some genetic disorders are caused by mutations in the DNA of genes. Other genetic disorders are caused by changes in the overall structure or number of chromosomes. A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as smoking, sunlight and radiation. Examples of Genetic Disorders: DOWN SYNDROME KLINEFELTER SYNDROME TURNER SYNDROME COLOR BLINDNESS HEMOPHILIA SICKLE-CELL DISEASE ALBINISM Cri du Chat SYNDROME CYSTIC FIBROSIS HUNTINGTON DISEASE  

Cystic fibrosis Genetic disorder in which the body produces abnormally thick mucous that builds up in the lungs and the intestines. It occurs when two mutated alleles are inherited, one from each parent. The mutation causes three bases to be removed from a DNA molecule.

Sickle Cell Anemia/Disease Genetic disease caused by a mutation that affects hemoglobin (blood protein). Red blood cells are sickle shaped instead of round and cannot carry enough oxygen to the body tissues. A codominant condition (normal allele and sickle-cell allele are present) produce normal and abnormal hemoglobin. No symptoms. A person with two sickle-cell alleles will have the disease. Heterozygous condition protects people from malaria because sickle cells infected with Plasmodium falciparum collapse.

Sickle Cell Anemia/Disease Sickle red blood cells live only 10-20 days instead of the normal 120 days. The damaged sickle red blood cells also clump together and stick to the walls of blood vessels, blocking blood flow. This can cause severe pain and permanent damage to the brain, heart, lungs, kidneys, liver, bones, and spleen. Sickle cell disease is most common in Africans and African-Americans.

HEMOPHILIA Hemophilia is a rare sex-linked disorder that affects blood clotting in the human body. Blood clots very slowly or not all. The danger of internal bleeding from small bumps or bruises is very high. It is caused by a recessive allele on the X chromosome. It occurs more frequently in males than in females.

Down Syndrome Down Syndrome – (Trisomy 21) 47 chromosomes, extra chromosome at pair #21. This genetic disorder, which varies in severity, causes lifelong intellectual disability and developmental delays, and in some people it causes health problems. Down syndrome is the most common genetic chromosomal disorder. Symptoms include : flattened facial features, small head, short neck, protruding tongue, upward slanting eyes, relatively short fingers and small hands and feet, short height.

How are Genetic Disorders Traced, Diagnosed, and Treated? Doctors use tools such as pedigrees, karyotypes, and genetic testing to trace and diagnose genetic disorders. People with genetic disorders are helped through medical care, education, and job training.

Pedigrees Chart or “family tree” that tracks how a trait is passed from parents to offspring. How to make a pedigree: Circles are for females. Squares are for males. Horizontal lines connecting a male and a female represent a marriage. Vertical line and brackets connect parent to offspring. A shaded circle or square indicates a person has the trait. A circle or square NOT shaded represents an individual who does NOT have the trait. Partial shade indicates a carrier – someone who is heterozygous for the trait.

GENETIC PEDIGREE

KARYOTYPES A karyotype is a picture of all the chromosomes in a person’s cell. A karyotype can reveal whether a person has the correct number of chromosomes in his or her cells. Genetic counselors help couples understand their chances of having a child with a particular genetic disorder. Karyotypes, pedigree charts and Punnett squares assist genetic counselors in their work.