Mendelian population. No mutation. No natural selection. No genetic drift. Random mating. Or migration.
Consanguineous marriages. Marriage between related individuals by common ancestor within few generations. Marriage between father daughter, mother and son, brother and sister practically don't exist.
Incest taboo exists in all cultures. But many culture allow first cousin marriages. First cousin marriage is the nearest consanguineous marriage allowed in human society.
Reduces heterozygosity. Recessive gene concentration increases.
studies on effect of consanguinity on fertility and mortality. Afzal & SP Sinha 1984 on Ansari Muslims. 8% more child mortality among inbred population. But studies by PS Rao among brahmins of Tamilnadu in Maharashtra did not find significant rise in mortality or fall in fertility. this maybe because South Indian brahmins have been practicing consanguinity for so long that harmful genes have been carried out.
Effect on IQ. Afzal and Sinha 1984. IQ of inbred children was lower. Social expressions like oral expression and smile was delayed.
But in breathing is not harmful if population is producing enough.
Effect. Inheritance of defective gene in which can be dominant co dominant or recessive gene. Creating genetic defects. Brachydactyly short singers autosomal dominant.
Increases recessive autosomal genes and its effect. Albinism due to lack of pigment that imports colour. Find in San Blaz Indians of panama.
Six fingered dwarfism. Recessive condition. Frequent in Amish of Lancaster Pennsylvania.
Inbreeding marriage 37% in Tamil Nadu 33% Andhra Pradesh. Found in Memon community Bohra community. Syed saiya Lucknow community.
Rizvi 1993 study.
Data on consanguinity were collected with the help of extended genealogies traced up to three generations from 1930 matings among Garia, one of the Muslim groups, living in the Baniyakuchi area of Sarthabari police station, Barpeta district, Assam, India. The data revealed that out of 1930 matings there are 123 consanguineous marriages, representing a frequency of 6.37 percent of consanguinity within this group. The inbreeding coefficient based on consanguineous matings is 0.0064 ± 0.001. The data related to reproductive performance of 1930 mothers who have completed their reproductive span, exhibit a decline in number of pregnancies among consanguineous matings (4.80 per mother when compared with non-consanguineous matings where it is 5.40 per mother). Similarly live borns per mother are lesser in number among consanguineous matings as compared to the control group derived from the same population living in the same area. Pre-reproductive deaths among live births were found to be high (0.46 percent) among consanguineous Garia Muslims. The present findings indicate increased risk of death to live-borns from unions of consanguineous spouses.